I've also never seen a dog "just snap" and attack someone. I have 2 pit bulls, a German shepherd, and a lab, plus a cattle dog foster dog. I've trained dogs for 52 years. I mostly train big breeds, commonly known as the more aggressive breeds. My female pit bull (84 pounds) loves everyone and is gentle, patient, and I can't imagine her ever hurting anyone. She works as a therapy dog. My male pit (82 pounds) is dog aggressive and can be aggressive towards a person who he perceives to have a weapon. Also, if he were in fear from someone he would try to protect himself. I muzzle him whenever I take him off our property and at home he is kept in the house or in the yard with a 6 foot high fence and the gates locked. He loves most visitors but I watch him closely and never leave him alone with one. My German shepherd is friendly to everyone and I also use her as a therapy dog. She acted a little timid the last time she worked at the old folks home though, so I haven't taken her there since. It was the first time she ever acted that way. (She's 5 years old.) My lab is friendly to everyone and she has an obedience degree and works as a therapy dog. Dogs usually have a reason for what they do. And if a dog is going to bite or attack, there are usually some red flags if a person is alert to them. I have only seen one dog that would suddenly attack with no warning or reason. It was a dog in our rescue and the rescue would have put it down but its foster mom adopted it and hired a dog behavior expert to work with it so it would be safe to have around her family. She keeps it away from other people and it is fine with her, her husband, and her kids. The dog would be dangerous to anyone else. The pit bull that killed the babysitter grandmother must not have seen her as a pack leader who was in charge. Dogs attack weak energy not pack leaders.
Aggressive breeds need to know there is a firm pack leader in charge and that they are NOT in charge. My male pit bull used to have to be sedated unconscious for anyone to cut his nails because he would bite anyone who tried. Three people working together at the vet couldn't get a muzzle on him. I spent 4 months doing behavior modification with him and now anyone can cut his nails. He will hold his front paws up one at a time for his nails to be cut and then he will lay down and put his back feet up so the back nails can be cut. When he was 4 months old, my husband and I together using all our strength couldn't hold him down on the floor for a time out. Now I point to the floor and tell him to lay on his side and put his head down and he does. When we bring home a new foster dog, the male pit wears a muzzle for a couple of days and drags a leash. Then once he accepts the new dog he is totally safe with it (but I don't leave him alone with it). He's great with all of my dogs and cats. You have to know your dog and use common sense.
