I use this also and it is a good way to burn fat, sprinting in intervals. I use a ball or the example jack used on the mill. both work well. you will put lot of work on the body but not as much on the bones. if you ever played sports, you can probably remember how brittle your ankles and feet felt after running so many laps. I never had the same pains when doing something like suicides n wind sprints. you exert yourself a lot faster, your lungs, muscles, etc but not where your feet n ankles are killing you 3 days later. you could base your exercise on the type of dog you have though. if he really likes to pace himself long runs might be a good idea. if he's explosive n has lot of speed then sprint intervals will be good.