I have a 5 year old female bullmastiff (Mel) and she has been aggressive since she was about two, but at that point she was my dads dog, she has very bad aggression especially towards smaller, furrier dogs. She is not spayed, but before you say she needs to be spayed, i must tell you that I have only had her for about 7 months and when I first took her on she was 58.6 kg (13.6 kg overweight) and the vet said they would not operate until she was at least 45kg, she was weighed this morning at the vet and is now 47.7 kg so should be ready to be spayed in the next 1-2 months. But in the meantime I bought her a muzzle today and I don’t want to just slap it on her and make her wear it on every walk for the rest of her life (if spaying doesn’t cure her aggression), if I could train her to be more sociable. So to get to the point how do you go about muzzle training a dog? Also I think I should add that I also have a 12 year old collie (Penny) who lives with us and pretty much rules the roost, and Mel shoulder barges any big dogs that come between her and me.