We named him Rex, but he runs around our 22 acres like Sea Biscuit. On 4/14/2011, Rex had a stroke, and he lost the use of the back half of his body. All Rex knew was that when the front end moved, the back end is supposed to follow. The Walkin' Wheels Cart is the best thing that we ever bought for him. It's the best "physical" and "mental" therapy aid out there, in my opinion. The All Terrain pneumatic tires in a large size made perfect "training wheels" in the beginning. It made the cart easier for Rex to move over our stone driveway and our property. One day Rex came home with two flat tires from flat out running over "everything", including thorns. That cart goes everywhere, so thank you for making it durable. Here we are almost one and a half years later, and I've ordered a spare front harness and some foam wheels in a large size. I figured I'd try those, because the small foam wheels are so durable, that they stand up to the punishment that my warrior dog puts them through. Gosh, just look at that smile!