There is a difference between using a muzzle while training your dog, and muzzle training. Is your dog overly aggressive or unpredictable?
Do you feel unsafe while training him? If so, use a muzzle, by all means. However, a muzzle is generally a frightening object to a dog unless introduced gradually. It makes him feel trapped and unprotected. If it can be avoided, it is best to train without limiting his ability to be a dog.
Most dogs view a training sessions as a game. It’s playtime! He obeys a command; he gets a treat, or praise, or an atta-boy. It’s attention, and dogs crave attention. They want to please you. It’s their nature.
To incorporate a muzzle into such a dog’s training would change everything. Your dog’s eagerness will plunge and he’ll become wary of training sessions. Do you want that? No? Then why take a perfectly cooperative, exuberant dog and muzzle him?
That being said, a muzzle does serve a purpose. If your dog is one who nips, snarls or bites when he is nervous, he needs to be muzzled for your own safety (and his, because should he bite you, that could open up a whole new set of problems!)
But again, if you are training him through positive behavior techniques, and praising and rewarding him, it seems unlikely that he would become overly anxious to the point of biting or nipping.
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If you do not feel comfortable training your dog yourself, perhaps a professional trainer is the answer. Just check their credentials first because pretty much anyone can bill themselves as a dog trainer; and even among well-qualified trainers there are varying methods and ideologies. You want to be sure your trainer uses methods of which you approve. The video on next page has over 195,893 views!!