Well, a yard won't exercise a dog. Very rarely will you come across a dog who will just exercise itself by running around out there. Our house isn't that big and my dogs don't even use the yard that much. They have a doggie door and can go out anytime they please, but the only time they go out is if they have to potty or if I go out. If I go out, then they'll go out and chase each other and play and we'll play some fetch.

I know somebody who has a high energy dog in an apartment, a border collie. The dog gets alot of exercise every day through running along side a bike with her owner and the dog was involved in herding (for fun, not sport). This dog was a great dog in the small apartment with no yard and was quite happy.

Although I wouldn't recommend to anybody to get a border collie and try to keep it an apartment, but if you have the dedication to do that kind of stuff and your an active person, then it can be done sucessfully.