Let's look at some facts. There are about 30 fatal dog attacks each year in the US and the number one breed is pit bulls, Rotweillers are second with German Shepherds right up there.
http://en.wikipedia.org/wiki/List_of_fatal_dog_attacks_in_the_United_States
If I am confronted out doors with a threatening pit bull, or other large dog, I am going to assume the worst, especially if I am with family. These are very aggressive animals that fear no one and do not back down to usual threats you can use against other dogs. You don't have to wait to get stabbed to be in fear of your life and in imminent danger of grave bodily harm or death to shoot in self defense. Likewise, are you really going to wait until you have one of these viscious dogs chomping on you. It could get out of hand quickly with them knocking you down and going for the throat.
In addition, not only do you have to worry about bite itself, it is the infection that always follows that could be the deadly part of the encounter. I am a physician and I took care of a man who was bit and scratched by his cat that had been shot in the eye with a BB by his neighbor. His arm was swollen to twice the size with scratch marks along his entire forearm. He had two bite marks on his thigh which was likewise markedly swollen. Bottom line, he would have been at high risk of death without the IV antibiotics that I gave him.
Please consider this when considering dog attacks. It is not just the bite that causes problems, it is what follows as well. That in my opinion qualifies as danger of death or grave bodily injury even from small dogs especially if people have underlying medical conditions.
The biggest issue is if the attack occurs within city limits where fire arm firing is prohibited. We had a dog attack in our neighborhood a couple of months ago where a large boxer attacked a woman walking. Actually there were three loose dogs in this attack including a Rotty mix. Fortunately, they picked on the wrong lady, she was walking her two pit bulls. A couple of weeks later, another couple walking their dog had to jump into a neighbors SUV to escape the same pack of three dogs loose once again. We had little help from the city and it is Kommifornia so the issue of even having self defense available makes it a sad situation.
The community service officer that is part of our neighborhood watch simply said call 911. Essentially all viable self defense methods against a dog attack ARE illegal here in LA county. I will be happy to be back in Idaho soon and escape to a land that recognizes self defense, especially against large dogs.