What can you do if a neighbor's unleashed dog charges at you?

Leave the knife and the ammonia at home and instead get a can of animal mace. It's legal, carrying a concealed knife is questionable, and if you end up using the mace you don't have to worry about accidentally causing serious injury to a child or yourself, or even the dog if his actions are misinterpreted. Yes, the dog needs to be confined, but he doesn't deserve to be stabbed in front of a bus full of school children because his owners didn't socialize him. A can of mace will be much more effective as it will actually prevent an attack, whereas the knife is only good once the dog has attacked and isn't letting go (an unlikely scenario as most dogs will bite and move around too much for you to get a safe shot at them). A squirt gun with ammonia won't do much to stop an attacking dog. The stream is too narrow and weak.