Definitely you need to do more obedience training with him. When he starts to get nippy, immediately stop, make him do "sit," then "down" and have him hold that fir a minute or so, keeping his attention on you. When things are calm again, you can give him the okay, and resume walking, but be prepared to stop and the minute he starts acting up. Walking is a reward, and it can be taken away for any misbehavior! You will have to be far more stubborn than him, and no be afraid to look silly to anyone watching, but you can work though this. A calm walk gets praise at the end, a contentious one is not terribly fun, and he will figure this out in time!