How do I get my maltesse puppy to stop nipping?

I am an animal trainer and don't believe in punishing animals OR "positive reinforcement" when they are doing wrong. When I have a puppy or dog for that matter,who nips or bites, While they are doing it, I softly grab the snout with my hand so that they can not open their mouth and say "no biting" in a strong voice. I don't think I've had to do this more than a dozen times to a dog and it stops. Don't spray water at them, don't hit them on the nose and by all means never give them a treat to stop a bad habit.