A rubber horse bucket chained off the ground to a post or fence. Not the cheapy colored buckets, the old, heavy rubber, kinda ugly, black ones. The pretty ones aren't as durable.
I have dogs that do the same thing and this was the best way I have found to stop it. A simple chain with a clip to secure it, off the ground a bit. I also make blocks of ice in cheap baking pans and toss those outside with the dogs when it's warm out. Endless entertainment for free, and it keeps them cool.
I second upping the exercise though, sounds like a bored dog amusing himself.