I'm going to attempt to cover domestic and wild animals as well as present lethal, non-lethal and preventative alternatives for dealing with them. This is by no means a definative or exhaustive list, these are just the methods that I've used or heard about being used sucessfully. I make no guarentees as to their efficacy in your specfic situation.
That being said let the lecture begin...
Step 1: Domestic Animals
The best way to get rid of a pet you don't want is to take it to your local animal shelter. There are many non-profit groups that run shelters for animals you can no longer care for. By simply opening the phone book or doing an internet search you can easily find one. They don't charge to take the pet and are usually very sympathetic. Some are "no-kill" shelters, meaning they won't euthanize the pet if it isn't adopted within a certain period of time.
If you have a pure-bred dog or cat variety another option is breed specfic rescues. These are groups that focus on one breed of cat or dog. If there is a breed there is a rescue for it. These groups will take the animals, and work to find them good homes. My wife and I work with a greyhound rescue and find it to be very rewarding. (Check out the Grey Hound Connection to find a group near you.)
I don't know much about large animals (e.g. horses) but I'm assuming rescues that deal with them exist as well. I'm sure a little research can turn one up. My brother had the good idea of checking with 4-H or Future Farmers of America for large animal rescues in your area.
Like most things in life prevention is the best way to avoid the problem. In order to avoid having to make a painful choice like this there are a couple of things you can do:
1) Don't impulse buy. I'm guilty of it myself. The damn creature is just so cute you buy it without thinking or researching. This is how you end up with an animal that isn't right for you or your lifestyle. Also be sure to look at your finances ahead of time. To properly care for a pet is costly. I heard somewhere that for each pet you have your annual expenses increase by $1000 (U.S.). So you need to decide if you can afford another mouth to feed, vaccinate, and provide vet care for before you buy.
2) Have your pet sterilized. Dogs and cats give birth to multiple offspring at a time. Multiply that by the above figure and ask yourself if it is really too much trouble to have your pets spayed or neutered. It also relieves you of having to make the painful choice of which adorable fluff-ball to give to the shelter. And many shelters will spay or neuter pets at reduced rates.
Step 2: Domestic Animals - Gone Wild
You could also live trap them and take them to a shelter (see below), however this can involve much greater risk to your safety as these guys will try and hurt you out of fear and may carry disease. Best to call animal control.
To prevent them from coming around see the steps below.
Step 3: Domestic Animals - Fish
As far as I knew when I first published this instructable, there were no shelters which take fish. Well it turns out I was wrong. Scammah and x86Daddy pointed out some options I hadn't considered which revealed a mammal-centric bias in my views. An internet search revealed the existance of fish rescues. (The same will probably hold true for reptiles and amphibians as well.) So before you jump to killing the fish, do more research than I did and see if there is a fish rescue in your area that will take your finned friend off your hands.
In order to get the fish to where you're dropping them off you can use bait buckets. These are intended to be used by fisherman to transport live bait, but they work well for moving pet fish as well. Plus many come with openings in the top so you can feed in air lines etc. to make temporary housing for your gilled compadre.
If you don't have a fish rescue in your area this leaves you with two options:
1) Release the fish to the wild. This is a really bad idea. It relieves you of the guilt of having killed the fish, but as most pet fish are non-native tropical species it will probably die anyway. Secondly, if the fish doesn't die you have just introduced a non-native species into an ecosystem. To understand the damage non-native species can do to an ecosystem do a little research about the Great Lakes in the United States or the continent of Australia.
2) Kill the fish. While unpleasent this is probably the best option from an ecosystem point of view. Most of folks (myself included) do this by flushing them down the toilet. If the fish is too large to ride the porcelan highway freezing is an option. Catch the sucker and put him in a container of water. Make sure you use a container with a tight fitting lid as the fish may flop around. Place the container in the freezer. Since fish are cold blooded it will just slowly reduce their metabolism until it stops (dies). Then dispose of the body in the trash on the day the trash is to be removed. If you throw them away earlier it will thaw out and begin to rot. This would lead to an unpleasent odor.
I'd encourage you not to poison the fish's water. It would kill the fish but you'd have to use a great deal of poison to overcome the dilution of the water. If you do use this option be sure to pull the charcol out of the filter. It would remove the poison from the water. Once you've poisoned the fish you're stuck with a great deal of poisonous water. Additionally the poison could bond to the aquarium and its contents making it unusable.
x86Daddy mentioned a method for euthanizing fish in his comments that is much more humane than the options I was aware of. He was gracious enough to let me add this information to my ible to make it a more complete resource. He suggested placing the fish in a small volume of water and then adding oil of clove. According to him in small doses it works as an anathestic and in large doses will kill the fish (see Paracelsus). I haven't tried it myself, but if I have a sick fish beyond help in the future I will definatley give it a try.
Step 4: Wild Animals - Disclaimer
Always remember that a wild animal, no matter how "cute", is dangerous. Nature is not the Utpoia portrayed by Disney films. Nature is a rough and tumble place where survival and reproduction are the two primary concerns. Wild animals will generally behave in a very nasty fashion, as they have no way of knowing, or caring about, your intentions. Always make your own safety a top priority.
Don't mess with a wild animal until you've done some research. That damn creature eating your garden may be endangered/protected and by messing with it in any way, shape, or form you could be subject to legal penalties including hefty fines.
Step 5: Wild Animals - Lethal - Firearms
The first thing you need to ask yourself is if you are comfortable with killing using a firearm. Shooting a living thing shouldn't be done lightly. Keep in mind killing is not as it is typically portrayed in the movies. It is rarely an instant death without suffering. Are you comfortable with seeing blood, tissue, shattered bones and organs? Are you comfortable smelling the blood and voided bowels? Can you stand seeing the animal writhing in pain and possibly hearing it scream in agony? However you answer this question it is something you should really ponder and answer honestly. If you commit yourself to killing an animal you cannot back out if you only wound it. It would irresposible and cruel to shoot an animal and then leave it to die slowly because you find it too upsetting to finish it off.
The second thing to consider is legality. As far as I know it is pretty much a universal no-no to discharge a firearm within city limits. So research your local ordinances and if it is illegal investigate other options. And if you're still pondering shooting a pesky critter, knowing it is illegal, remember a motto that has served me well: "I am WAY too cute to go to prison!".
Now if you're comfortable with shooting an animal and in a place where it is legal your third consideration should be the weapon. You want to use a weapon and type of bullet that will actually kill the animal. Shooting a really big animal with a small bullet more than likely won't kill it. It will just wound it leading to a slow death by wound complications or starvation. In this same vein don't use an air rifle. I know they can attain lethal velocities but using good old cordite propelled rounds of the approprite caliber is a much safer bet.
Another factor is the type of round. If you're using a rifle I would encourage you to invest in jacketed hollow point rounds. A hit with this type of bullet is much more likely to be fatal. If you're using a shotgun the size of the shot will depend on the size of the prey. Or if it is a deer use a deer slug. I'm not very knowledgeable about shot size versus prey relationships so if you're going to use a shotgun you'll have to find someone more knowlegdeable than I.
If you are unsure if the weapon you have will kill the animal get some advice from an experienced hunter or a trusted gun store employee. If in doubt don't shoot the animal.
Related to using the approprite weapon, you must ask and answer a couple of further questions:
1) Am I skilled enough to hit the animal in a lethal spot? Make sure you are familiar with the weapon and can hit what you're aiming at. (You may also want to study its anatomy so you know where to aim).
2) Am I skilled enough to hit the animal while it is moving? If not you'll want to hit it from ambush, which will require patience and waiting. Or instead of using a rifle switch to a shotgun loaded with an appropriate shot shell. The multpile pieces of shot will greatly increase your chance of hitting the animal.
3) Is the physical location where I'm going to shoot the animal clear of people and richochet risks? Remember bullets can travel great distances. It is best to fire in an area that is well cleared of people and things you don't want to put holes in. Also be aware that bullets can richochet (to varying degrees) off rocks, metal, water and glass so be aware of what is in the background of your target. If you don't know don't shoot!!!
4) If you don't have experience with firearms, don't use one. Get someone to teach you how to safely handle the weapon. There are courses you can sign up for or have someone with this experience teach you. I think you can even find an Instructable on the subject.
Step 6: Wild Animals - Lethal - Poison
A method my uncle used for mice is uncooked instant mashed potatoes. The mice eat the instant potatoes which expand in their stomach which crushes their organs. I imagine this might work for other small rodents.
This next method is not recommended but for the sake of completeness I'll mention it. A different uncle killed of a family of groundhogs using chlorine gas. He blocked off all the entrances to the burrow except one. He then poured ammonia and bleach down the hole which generated chlorine gas and suffocated/burned the lungs of the groundhogs. This gas can do the same to people and to use it would be exceptionally risky if not downright stupid.
There are many available insect baits that all work well. Some of these are liquids that illustrate one of the main drawbacks of poisoned baits. The ones that look like honey have appeared enticing to children and they end up getting poisoned instead. This is the main draw back of poison; it is less specific than aiming a gun and can kill things you don't intend to such as domestic animals, beneficial insects and humans.
Step 7: Wild Animals - Lethal/Non-Lethal - Animals
The downside is your animals can be injured which leads to increased veterinary bills.
Another alternative is to release wild predators of the pest animal into your garden. I've heard of people releasing ladybugs and their larva to eat aphids and praying mantises to control other insects.
However, the downside to this is they are even less specific than poison as they are independently acting creatures with their own desires so they may not stick around or they may decide to eat things you don't want them to eat. Also both introduced domestic and wild animals have overrun and destroyed entire ecosystems. So don't introduce species that aren't already present. See the aforementioned comments about the Great Lakes and Australia.
Step 8: Wild Animals - Lethal/Non-Lethal - Traps
Non-lethal traps (live traps) come in all sizes. It is typically a cage with a spring loaded door. You place the bait behind the trigger and when the animal enters the trap is closes behind them. You can then relocate the animal to some place else. They come in many sizes ranging from tiny for chipmunks up to huge for coyotes. However, be sure you have the permission of whoever owns the land before you release the animal. Please check local ordinances as well. In my home state it is illegal to release a raccoon trapped in one county into a different county unless it has been quarantined for 90 days. (This is intended to prevent the spread of rabies.)
Consider draping an old blanket over the cage during transport. Just the sight of humans tends to make wild animals freak out. It is not unheard of that animals actually can die from stress.
Be aware there is a greater chance of injury using traps. The animal is frightened and possibly hurt so they won't be too happy to see a giant hairless monkey showing up to devil with them. The animal won't know if you're intent on releasing it unharmed or beating it to death with a pipe, so wear gloves and other heavy protective clothing as they may try and bite you when you are moving the cage, covering it with a blanket or during the release process. When you release them open the door and then back off. Let the animal come out on its own. Trying to force them out will just end badly and increase the stress level.
Whether you're live trapping or lethal trapping bait is key. I've found that raccoons and chipmunks really dig peanut butter. If in doubt do some research and a little trial and error experimentation in order to find an effective bait.
A note on Japanese Beetle traps. These are bags treated with pheromones that draw the beetles in. Once they're in the bag they can't get out and they starve. However, according to my Mom (degree in horticulture and long-term Japanese Beetle killer) the pheromones in the trap end up attracting more beetles to your yard. So she recommends convincing a neighbor to put the trap in their yard to draw them away from yours.
Step 9: Wild/Domestic Animals - Non-Lethal - Deterants
Scare Crow: The most traditional deterrent is the scarecrow. A big scary thing that keeps animals away from crops. The modern version are the plastic owls. The down side to these is that the animals become used to them, especially if they are always in the same place, so they ignore them and eat what they want.
My Dad uses a variation on the scarecrow theme. He drills a hole in the edge of CD's and suspends them from a rack above the plants he wants to protect. The moving of the CD's in the wind and reflection of the light from the underside drives off the birds.
Pepper: Pepper is great for deterring small rodents. I've heard of people mixing it into their bird seed to keep the rodents from eating it. The pepper will burn the mucous membranes in the rodents' mouths but doesn't affect the birds' beaks. I've also used it with great success to keep them from digging in flower pots. When you bury a pet who has shuffled off the mortal coil pour copious amounts pepper over them. This will help keep scavangers from disturbing the body. I've used black pepper for this, but anything hot and spciy would probably do the trick.
Barrier: Building a barrier to keep the animals out is also an option. A friend of my aunt's drove Canada Geese out their yard by building a minature fence out of fishing line. They placed stakes around their pond and then strung fishing line around the perimeter a few inches off the ground. The geese couldn't step over the line to get from the pond to the yard (and vice versa) so they left.
Human Scent: Wild animals get really freaked out by the smell of people and leave. I've heard of people sprinkling human hair from the barber shop around their gardens. I've heard of folks urinating around the perimeter of their gardens to scare animals off.
Step 10: All Animals - Non-Lethal - Preventative
The following is a list of simple preventative measures that can save you pest troubles:
- Seal food in air-tight containers
- Use trash cans with securable lids
- Plug open spaces around wall penetrations
- Store bird seed in air-tight containers inside your home
- Cover external vent openings/chimney with grill work
- Dispose of nests and the animals move on
Step 11: Body Disposal
Some veterinarians have crematories or contracts with crematories so if you sweet talk them maybe they'd be willing to take your body. (Potential double entendre).
Step 12: Summary/Conclusion
The key to dealing with animals is research and observation. By knowing their behavior you can more effectively deal with them. And before you do anything make sure what you're considering is legal. More than likely you, like me, are way to cute to go to prison.