Thanks for all the info.
I did put a lot of thought into muzzling him. And yes I did it because he has shown threatening signs such as lunging, growling, and he also nipped someone once. I have had him since he was a puppy but he just recently shown this behavior when a trainer unexpectedly lost her cool and started jerking him harshly around. When we interviewed her she seemed great(in my defence). We have contacted a professional and have been working hard to socialize him again. He was doing really good and hardly needed it any more. However, we live up north and since he has almost no fur he cannot walk much for the six months it is -50 degrees. Since it is a small town there is also no socializing or indoor groups. We have arranged play dates, but mostly with the same people. When it finally warmed up he was showing mild signs of his former aggression. Just to be safe we put the muzzle on again. After only two or three walks he seemed to remember his former training and returned to his happy, social self. However I would like to get him accustomed to wearing one on walks so if he ever needs it again it won't be a big deal. Also he has this habit of eating seagull feathers, which could have some sort of disease which he needs to be muzzled for if were walking where there are lots of them.