First off, a dog’s skull has evolved over millions of years to be a weapon. When a dog gets into a fight with another dog, where do they bite each other? In the head and throat. No matter how strong you think you are, punching a dog in the nose or eyes isn’t going to stop it from attacking you. It’s just going to make it angrier. That area of their body has evolved to take massive abuse. Also, any breed of dog that you’d be worried about attacking you has a “switch” in their brain that turns off pain when they go into attack mode. Think about all those gruesome aftermath pictures of dog fights. You see these dogs with their faces ripped off and those were the ones that won the fight! So if a dog can still tear you to pieces with half its face falling off then you can be damn sure poking it in the eye isn’t going to stop it.
With that out of the way, the most vulnerable part of a dog is their abdomen. You can very easily stop an aggressive dog (even kill it) by kicking it in the stomach under the ribs. It’s the same spot where you would punch a human if you were trying to knock the wind out of them. So if you see a dog attacking someone and you want it to stop, give it one solid kick in the stomach. It doesn’t matter how bad ass the dog is — a 14-year old girl will stop it in its track with a good kick in the right spot.
Now if a dog attacks you, chances are it will go for your head or throat and try to bite it. A dog will almost always have to lunge at you to attack. Use this opportunity to side-step and kick it in the stomach area. Again, one swift kick will make most dogs retreat in pain. Repeat this process until it leaves or succumbs to injuries. If you have a walking stick, cane, umbrella, etc., whack the dog very hard on the top of its head. This acts as a deterrent without causing grave injury to the animal (remember — they have very tough noggins).
If you’re on the ground and do not have any other options (read: worst-case scenario), you have to let it bite your arm like in those videos of cops training K9s. Then when it grabs your forearm, reach around its head with your other arm and shove your forearm deeper down its throat and hold it there with your other arm. For dogs, this is similar to holding an alligator’s mouth shut. When your arm is pushed all the way down their throat, they can’t do anything about it. You just have to hold it there with your other arm so they don’t get a chance to bite something else. From there, depending on if it’s a friend’s dog or some random dog that went crazy, you can kill it by kneeing it in the stomach.