I live on a dairy farm and we have thousands of tires stock piled for covering the corn silos filled with feed silage. We do all kinds of things with tires, you just have to check the tire for steel belting as the little metal wires will poke and cut you if the tire is real worn or rotted. I have built fish ponds and planter gardens out of them, we had a sand box as kids made out of a tractor tire. I put the rubber feed dishes in them to prevent the horses from tipping them over. My husband built a retaining wall out of them once! I feed round bales out of a giant tractor tire to my beef cows, I gave the goats a few to play with and they sleep curled up inside of them. You can build horse jumps as already mentioned, we used to ride our horses through tires on the ground as kids (like foot ball players run through them lifting their feet real high) but I do not think a lot of people still incorporate those obstacles into their trail courses, but you still can. Stack them up like barrels and have a barrel race, make obstacles or weave poles, or bury them half way into the ground and make a garden fence. The possibilities are endless. You just cannot throw them away, as its real costly, its like, 3 dollars per car tire here to throw them away at the dump!