I was out walking my dog after dinner one night a few years ago. My neighbor at the time (6 doors down), was out in his yard with his two dogs off leash. I was on the oppositie side of the street and my dog was on a leash.
When his dogs saw us, both came at us snarling and at a dead run.
I put my hand on the grip of my 357 mag snub that was in my pocket, and in a very loud and aggressive voice said NO! Both dogs slowed down and stopped snarling. Then the owner calls them back and apologizes. 
I told him that if he wanted his dogs to stay healthy, he'd get a tie-off or keep them in the fenced back yard. Cars are always speeding down the street don't ya know.
Lethal force was definitely forthcoming if they'd continued their charge. I've been charged by a single agressive dog more than once and was able to control it without injury to myself or the dog but not two and I know what two dogs are capable of.
My dog is my best friend, a part of this family, and will be defended as such.