Tires make excellent animal pens for your four legged friends, as well as for ducks, geese and other birds that do not fly! After calling the EPA, we learned that they are not even a hazard to the soil around them (but you probably don't want to plant into them). The shelter in the pen keeps out snow and rain, and was constructed out of waste lumber, an old tarp and plenty of new screws and new 1 inch washers, a total cost of new materials of about $40. The tires were free under a beneficial use program designed to encourage the recycling of tires into useful things.
Just started a discussion about this sort of thing - the recycling of waste materials into useful things! Let us know how you recycle!