I had recommended hot pepper as a non-toxic dog deterrent. Recent reports indicate that it can actually be harmful to dogs. There may be ways to use it safely, but until I learn more about the problems that have been reported, I'm recommending against doing this, and leaving this instructable up only to help spread the word about the problems.
Hot peppers are a well known approach to deterring dogs from relieving themselves where you don't want to step in it. It's effective, and I thought it was no more toxic to dogs than it is to people. But that may not be true.
The idea of this instructable was to help keep the pepper in place--if you just sprinkle Tabasco sauce or cayenne powder, it's likely to wash away (if it's rainy) or blow away (if it's not). My solution was to mix cayenne powder with oil, and dribble that on the ground around the area you want to protect. The oil not only helps prevent the rain from washing it away (and the wind from blowing it away), but it also helps bring out the capsaicin, the active chemical in hot peppers, which is soluble in oil but not in water.
It worked for us to solve a regular problem, and lasted through at least several days of very heavy rain.
We never had any indication that it was harming dogs or wildlife. My assumption was that the dogs were using their noses to avoid it, and were not eating it. And that even if they did, it would be unpleasant and not harmful. As a regular consumer of a lot hot peppers myself, I didn't think there was potential for real harm. Unlike a chemical burn, the "burn" of hot pepper is a perceptual trick, not a result of physical harm. But this seems to have been wrong...I'll add more information here as I learn more.
Step 1: Ingredients
If you buy cayenne in fancy bottles, it can be pretty expensive, as much as $75 per pound , including shipping. But if you buy it from the bulk section of a grocery store, or in bulk packs with free shipping from Amazon, it can be less than 1/10 the price. Avoid getting too large a package, because its strength will decay with time after the package is opened. Two 1-lb. packages from Amazon for $14.24 seems like a great deal, if you are serious about this. Each pound is good for dozens of applications. Or you could opt for the organic variety .
For oil, you could use any vegetable oil you have handy. I used mustard oil , because I had a bottle of it around, and I thought it might help deter dogs. (I bought it for cooking, but haven't used for cooking after reading about occasional problems with it being mixed with Argemone mexicana oil , which is toxic, and because the bottles you can buy in the US are labeled for external use only, it's hard to be confident that it has been carefully prepared to food-grade standards. But I digress--any vegetable oil will work.
The wildflowers aren't needed for anything, but why not? Anything's better with wildflowers.
Step 2: Mix
Mix three parts of oil to two parts of cayenne. I used 3 fluid ounces of oil with a quarter cup of cayenne. The proportions are not critical –you can simply eyeball it by first putting the cayenne in a jar, and then filling with oil until it comes up about twice as far as the cayenne did alone (as shown left). Use an glass jar with a lid that caps tightly so you can shake it to mix.
Step 3: Dribble in the Problem Area
When you are done, wash your hands well, especially if you haven't worn gloves, before you accidentally rub your eyes or touch any sensitive skin.
So far it has worked--we used to have fresh deposits in this area pretty much daily, and the only new poop we got in two weeks was about 5-6 feet away from the area I outlined. I then made a new batch and treated that area, and zero new poop since then. It's lasted through several days of heavy rain.