Next: an untrained dog attacking a person will jump up at your throat. That's when he's most vulnerable to a knife-based defense at his throat or chest.
Sorry, but mostly untrue...Most will go for an arm or a leg...I've trained dogs with "high defense" drives, and most will take what they can "safely" get. If they come in high they know they are vulnerable....Usually they "get in and get out" quickly, then re-attack if still threatened. They will go for head/throat if you are on the ground, but otherwise will take an easier target.
The classic defense is to wrap something around your off forearm, feed it that and then stab it in the throat when it locks on. Untrained will lock, trained will disengage and come back
OK, TOTALLY wrong. Trained dogs are trained to bite and HOLD on for dear life. My trained dogs will hold on to a "sleeve" until they drop dead from exhaustion. Even after the "decoy" has let go of the sleeve. The ones with high defense, will let go of the sleeve and go for a leg (or crotch), as soon as the sleeve stops moving (its a prey object). And, you better have something VERY substantial to wrap around your arm...My prize Shutzhund dog can crush a competition sleeve (which is VERY heavily constucted) to the point where it is difficult to get the sleeve off your arm...He'll even leave bruises. And this is a German Shepherd which doesn't have the jaw strength of, say, a Rottweiler or Mastiff. A big dog, with a full grip will break the bones in your arm, even with alot of padding.
I would never try to "fight" a big dog with a knife...They can move too fast, and absorb an incredible amount of damage. You might get lucky, but I wouldn't bet on it. (And yes, I've had to fight a dog on occasion, while training. Best just to get outa the way of his/her teeth. I have grabbed a couple by the throat, when I got an opening, and while squeezing HARD to cut off their breath, pinned them to the ground. Again, don't try this at home!)
Case in point: I worked in a garage, years ago where we had a BIG German Shepherd as a guard dog. Some dirt bag broke in and the dog went after him. The BG stabbed the dog 4 times in the chest and stomach. Dog survived...They took the BG (after he managed to escape back out a window) outa there on a stretcher.. He pretty much looked like hamburger.