A muzzle is not for aggressive dogs. It is needed on public transport, at the vet, when travelling, at appointments — and under the rules for walking dogs in public places. A dog trained to a muzzle calmly and in advance takes all of that in its stride. A dog that has one forced on for the first time on the day it is needed remembers both the muzzle and the occasion.
Which one to choose
A basket muzzle, metal or plastic, in which the dog can open its mouth fully, pant and drink. This matters: dogs cool themselves by panting, and a muzzle that holds the jaws shut is dangerous in summer.
Fabric muzzles that clamp the mouth closed are for a few minutes at the vet only — never for walking, and certainly not for running.
Sizing: leave clearance between the nose and the walls, the mouth should open freely, the tongue should fit. A dog will always work a tight muzzle off, and rightly so.
Seven days
Day one. Just show the muzzle and put it on the floor. The dog approaches and sniffs — praise, treat. Nothing goes on.
Day two. Hold the muzzle in your hand with a treat inside. The dog puts its own nose in to reach it. Got it, came out, celebration. Repeat a few times, half a minute per go.
Day three. The same, but feed treats through the basket while the nose is inside. The goal is for the dog to hold its nose in slightly longer, by choice.
Day four. Fasten the strap for one second and take it straight off while the dog is still chewing. Repeat, working up to five or ten seconds.
Day five. Put it on and immediately do something enjoyable: play, go to the kitchen, head out for a walk. The muzzle should predict good things, not a vet appointment.
Days six and seven. Short walks in the muzzle, five to ten minutes, then off. Increase gradually.
The main mistakes
Rushing. If the dog turns its head away, freezes, licks its lips or yawns, you are moving too fast. Go back a step and stay there a day or two.
Forcing it on. Hold the dog down and buckle it once, and all the previous work is undone.
Using it only before something unpleasant. If the muzzle appears only on the way to the vet, the dog will connect the two within two repetitions.
Leaving the dog unsupervised. A muzzled dog should not be left alone: it can snag on something.