By the way, my black lab, a nine-year-old, will not let anyone near my children or me when my husband is away - he will growl and then bite if you get too close. It is your responsibility to know the nature of your dog - not just its breed!
That being said, ain't it great to have armed neighbors!
What your vet told you is true. When we lived out in the rurals, local farm dogs would get together in the morning and go off on jaunts together. Individually, these dogs were fine, but as a pack, they shagged small cattle, goats and chickens.
We have a Great Pyranese guard dog out in the fields with the sheep. He will kill anything that goes in there without me being around. We have coyote and wolf problems around here. Not any more at my place. And any LEO who ever thinks he's going to go wandering around my place will be mighty sorry. The DNR man did that two years back. Instead of asking me to gain access to my property to look at whatever he was interested in, he just climbed the fence and walked a hundred feet into the pasture. A neighbor called to inform me that she saw a man in a tree in my pasture. He was all lippy at me telling me he could shoot my dog. I told him he could just stay there then. A dog is not an easy handgun target when facing you. After he did get down, I wrote the DNR complaining of trespass. No response though.