Watch from about 31:00 min on. Ellis talks about how medium drive dogs that have some drive, but perhaps not enough to totally focus or "do anything for" the reward (retrieve), recieve the brunt of his compulsion training out of neccessity. He goes on to say with self reinforcing behiavors (chasing squirrels etc), non-reinforcement does not work. It only goes away with punishment. He does say he tries to block the behavior as much as possible.
He also talks about how he experimented with positive only training for a couple of years and the disaster it caused, thus he went back to the use of some aversives/compulsion. Belief it or not, he talks about how dogs need to learn how to turn pressure off. Very interesting stuff that is presented in a easy to understand manner.