I just started basic obedience for storm. my trainer comes highly recommended and has 40 years experience in training dogs. he is an ex canine cop. however, he recommends that i get myself a muzzle. i personally have my sights on a leather one, but was wondering would the nylon be better. he has never bitten anyone before, but has fear aggression and cannot be trusted when approached by strangers? what do you recommend as the best. i've also heard that the dog should be able to pant and drink water.