When I hear the word ‘nipping’ I think of puppies not understanding boundaries yet. That’s different from biting which is usually a behavior meant to increase distance between the dog and the person being bitten. Muzzles can be positively conditioned so that pups like wearing them. All pups should be conditioned to wear a muzzle. A muzzle isn’t used to correct behavior, but can be used as an extra layer of safety in case you make a training mistake. If your dog has a history of showing it’s teeth, growling, snapping, or biting, you need to seek the counsel of a veterinary behaviorist or certified behavior consultant.