My horse has a nipping problem?

Ah, my guy can be like that. With horses who get lippy, since it can transition to them biting, I don't allow them to lip. Give him a "love tap" on the nose with your hand. Won't hurt him, it'll just snap them out of it and they'll be like "whoa I did something wrong! Better not do that again!" But be consistent because they don't learn from the first time :)