Is it a grazing muzzle or an anti-biting muzzle? If it is a grazing muzzle, that would be good, but if the horse has a buddy, they can learn to take it off.
It might also be handy to have a gate on your run-in, that way if a fence breaks or you want to keep them off the pasture completely for a while, you can keep them in there.
Intermediate Rider~Learning Equitation and English Pleasure~Interested in Eventing
A horse will tell you everything you need to know about him, if you listen.