I've been working with a border collie from my flyball team with serious ball obsession. He is so obsessed that he imagines balls that aren't there. He especially loves going for moving balls, which isn't great for flyball. I've seen people run dogs that are chasing balls all over the place in the run back and it's dangerous and looks stressful. The main thing I always hear is keep tennis balls away from the dog outside of flyball. I understand this to a point. You don't want to constantly play ball with a dog that you are trying to convince to NOT find tennis balls highly rewarding. On the other hand, you don't want to deprive them of something they love, so that when they finally see one they freak out and obsess even more.
What has been working is overwhelming him with tennis balls at home. He sleeps in a crate full of tennis balls and over several weeks has gotten less and less obsessed with those balls. He is also getting good at "leave it" when someone is bouncing a ball. We've been playing a game with him to build tug drive. You throw the tug out about 5 feet, restrain the dog and then race him to the tug. You beat him to the tug two times and don't let him get it. On the third time you get it, but then run away and get him to chase and get the tug. By this time he wants the tug BAD! This works well. It would be helpful for anyone looking to build tug drive.
I think I might also try "Its Yer Choice". I've been playing this game of impulse control with my dogs and it works really well. Also I'm signed up for Susan Garretts Recall Class., maybe that will give him some ideas!