A dog taught not to pull with one of these collars must continue to wear it-usually for months or years,and sometimes for life-as pulling on leash is easily relearned once the collar is off.And,if their owners alternate back and forth,the dog may lear that it is dangerous to pull when the choke or prong collar is on but safe to pull when it's off and so adjusts his behaviour accordingly.This is a function of how animals learn not an example for dogs being "bad".