There are many Instructables (and other Web pages) on using tires (tyres, but I'll use the other spelling) for gardens, which I have been very motivated by, but here is how I used two tractor front tires to build a fish pond. The original inhabitants were our two surviving bronze goldfish, who after years inside, finally bred in the pond and had three babies.
This pond was built in December 2007 in the earlier days of my turn-the-front-lawn-into-garden project.
The tires came from a park mowing tractor so are wider than normal tractor tires, giving extra height to the pond. You can usually pick these up free, in New Zealand anyway, from large tire repair and supply workshops: mine came from the parks maintenance company I work for - free disposal for them and free supply for me!

Materials:
two tractor tires (one, two, tractor, car - your choice)
large cardboard box, old carpet, etc
sand
newspaper
thick polythene sheet from a local BORG (Big Orange Retail Giant)
flexible drainage coil (I had this lying around)
geotextile (eg weedmat, mudstop, etc) [oh, or you could use old carpet!]
wire mesh
fencing wire
soil, container mix, or compost
water
fish
water plants and land plants
two terracotta pots

Tools:
spade
bucket
hose
clamps
reciprocating saw, jigsaw, hacksaw or even a sharp sturdy knife
short length of 25mm PVC pipe
craft knife
tape measure
stapler

Step 1: Cut Sidewalls From Tires

I haven't gone into tire cutting detail here, as there are other Instructables that deal with this (eg auntwrenny, who thinks much the same as I do about leaving one sidewall on: https://www.instructables.com/id/Used-Tired-Raised-Garden-amp-Tree-Ring/). I used a reciprocating saw for this step, but a sturdy sharp knife would probably do it with a lot more effort. A small amount of frequently applied water helps as a lubricant. Remember the proximity of electricity: if you kill yourself, don't say I didn't warn you.
Cut one sidewall from one tire and both walls from the other, leaving about a 75mm (3 inch) lip. I only cut out the upper wall of the second tire at first, but the polythene would not mould around the convoluted 3D-ness of this arrangement. Unfortunately, I did not take photos of the second try, but you'll get the idea.
Smaller tires can be done with a jigsaw or even a small knife: see the paring knife I used on car tires (thanks for the use Sweetie ... oh, I thought I'd asked you about that?... oh ... er ...).

Step 2: Lay First Tire

It is vitally important to get the pond area level, firm, and in the right place because the water level will shout out your laziness, soft soil will subside under the pond's weight, and you will NOT be shifting this anywhere!
Lay the first tire complete sidewall down on the flattened cardboard box to help protect against sharp things.
Fill the hole with sand until it is level with the lip of the bottom rim.
Thickly layer newspaper over the bottom and up the sides as best you can (damp paper sticks to the wall better).

Step 3: Add Second Tire

The lip you leave on the first tire will provide plenty of support for the lower lip of the second tire. As best you can, tuck newspaper into and around the cut sidewalls to help protect the polythene (this may seem tedious or unnecessary, but consider how tedious and unnecessary a leak would be).
Make sure the tire is sitting firmly.

Step 4: Insert Polythene Lining

This went a lot better once the 2nd and 3rd sidewalls were cut back!
Insert the polythene so that a roughly even amount is poking out the top all around. To estimate the size of the plastic, I had run a string progessively down one inside wall of the pond, around the bends, across the floor and up the other side, then added 300mm (12 inches) for safety.
Fill the pond to about 3/4 up the second tire. The polythene will look terribly crumpled, but that's life.

Step 5: Clip Polythene to Lip With Drainage Pipe

Cut a slit down the length of the drainage pipe with your reciprocating saw, jigsaw, handsaw or whatever. I cut the pipe somewhat over-length, just in case, even though I'd measured the rim.
Press it over the pond lip, trapping the polythene, then apply a clamp (or preferably use a helper; dogs do not qualify). Using a clamp or two to hold the polythene until you get to it can help.
Insert the PVC pipe to keep the slit open and work your way around the tire applying more clamps or helpers as you go.
When you get to the end, match up the two pipe ends and cut the last one to length.
Use a sharp knife to trim the excess plastic. I should have filled the pond further than I did, but fortunately there was enough slack for the polythene not to pull out of the drainage pipe when I did fill the pond.

Step 6: Voila! Pond. Add Plants and Fish

This is where the levelness of the pond's foundation tells the world about your diligence.
Boy, this was a proud moment!
To raise the aquatic plant to a more appropriate depth, I used a large upside-down terracotta pot.
About 6 weeks of summer later near the end of Jan 08, the pond was a going concern with happy fishes. All summer I used the water to water the vegetables: fish wastes are fertiliser. As the garden took most of the pond, the water is regularly topped up with fresh water. Because of this I have not needed to filter the water. Algal growth was a problem until I allowed Azolla to cover the surface, thus cutting down the light.
As the garden got bigger, I built a pumped system to empty the pond, but that's another story.

Step 7: Add Soil Retaining Fence

I used plastic mesh for this 'cos I'm a cheapskate, but that was a mistake as the pressure from the wet soil has started to break the mesh. Use plastic-coated wire mesh.
Use highschool geometry to estimate the length of mesh or do like me and just wrap it around the pond with a bit of overlap until it looks about right. Allow for 100 - 200mm (4 - 8 inches) between the pond and the mesh.
Staple the geo-textile on to the mesh to hold it in place while erecting the fence. I left a space at the top for plants to climb on, but should not have as the textile has dragged down over the months and is now too low.
Pin the ends of the mesh together with a doubled-over length of fencing wire (New Zealand's famous No. 8 wire is perfect for this! Look this up: it epitomises the Instructables philosophy also).
Carefully fill the resulting space with soil, watering it down as you go. In the photo, my geotextile wasn't high enough so I couldn't fill it right up.
Plant the top, and/or cut slits in the side (at the top of a mesh square to allow for downward creep of the texile) to insert cuttings or divisions. I started with begonias and herbs.

Step 8: Pond Updates

The pond is going well and needs virtually no maintenance over winter (in Auckland we get frosts but no snow). I just feed the fish every day before I leave for work. I have considered all sorts of filter systems or even aquaponics (still might do this), but using the water for the garden deals with those problems anyway.

This is my first 'able, though I've been a member for ages. Positive feedback and constructive criticism are welcome.

Here are some additions from my responses to readers' comments:

A couple of car tyres (to use the correct spelling... ;] ) would do as a small pond, and would be easy to move once empty (especially if it was on a sheet of ply or a pallet, and the soil step was foregone). A rule of thumb, I understand, is to have the most water possible per fish, otherwise you'd need filters and aerators, etc. If you did not put the soil around it, you may have to paint it white or shade it in summer (and then you could take the shade away in winter so the tyres warm up and stop the pond from freezing!).

I've seen a lot of those YouTubes, Instructables, etc on turning tyres inside out: if you look closely in photo 1 you can see where I tried this for the top tyre of the planter behind the pond with the banana palms in. Personally I don't do this because: I don't like the look, I don't gain enough in volume to warrant the effort, I always leave the bottom sidewall on to help with water retention during summer (also helps keep the soil in if I have to drag the planter anywhere), and can you even IMAGINE doing that with tractor tyres??!!!

I have thought about syphons and pumps etc, but I used to just use a watering can and scoop the water out. This was OK while the garden was small, but last summer (NZ is now in winter), I got our old swimming pool pump from storage (... NEVER throw anything out ...), bought fittings from the BORG, and started using that. It has the added benefit of sucking out the detritus from the bottom. Earlier on I had to siphon the entire pond out to get the crud and refill it totally. I might get organised next summer and set up an aquaculture system, with the ability to divert the water to a hose for the garden.

Step 9: Get Published in a Gardening Magazine! :]

The editor of UK's excellent Garden Answers* magazine noticed this Instructable and liked the idea so much she wanted to include it in the June 2013 issue! Well, wot's a humble fellow like me to do? So I said OK...

:]

* http://www.gardenanswersmagazine.co.uk/