Turn your collar up hot take him to a place were you know there are rabbits when he chases don't say anything hit him with the collar. I mean hold the button down until he breaks chase. If he chases again repeat the process. The key is not to acklowedge the rabbit. Let something strike from above. I had a professional trainer tell that is how he breaks them from chasing deer rabbits etc. It works.
Greatlawn
Exactly right. I have done this with every dog I have owned since I bought my first Tritronics collar in the late 80's. Rabbits, deer, cattle, anything I don't want them to mess with. It doesn't take long for them to quit. Just nail them hard and keep your mouth shut. That crap about how they used to do it is unecessary these days, that's why they invented the collar.