Treadmills -- Sprints or slow and steady

I'll get some pics for ya, but my partner has an old axle buried in the ground. It has 2 arms on it. 1 holds the dog on a snap and the other has a small cage on it. We put a chicken in the cage to start the puppies on it and a small pig to start the grown dogs. After they run it once or twice you can do away with the chicken/pig and they'll run on there own. Didn't taken em very long to figure it out and now they have a good beaten down track. It works great, he runs em till they slow down and puts another 1 on there by the time you get done with all of em the 1st one is ready again. They work themselves out.