You can now buy a treadmill specifically designed for dogs, like the Total Pet Health Exercising Dog Treadmill. As people work longer hours, live in places that don't allow them to exercise their dogs, and their dogs become overweight, more and more people are turning to treadmills designed specifically for dogs. (Be sure to use the ones designed for dogs as using treadmills designed for people may injure your dog.)

Just keep in mind that dogs love other types of exercise like walks and playing catch. So while a doggie treadmill might be necessary to keep them in shape given your lifestyle, if at all possible let them exercise in a way that they consider fun, not work! (Just wish I loved walking and playing catch as much as they do!)