When should you use a muzzle on a dog?

A muzzle should only be used as a safety backup. In some places, it's the law to muzzle your dog when out walking. A muzzle is sometimes used at the vet's office for nervous dogs who may bite. A muzzle is not a substitute for training a dog. It can often make an aggressive dog more so. Use it only if you know circumstance will warrant it.