I have asthma, and a deadly allergy to the stuff in pepper spray. Also to jalapeno peppers in Mexican restaurants. I almost died once when a restaurant cooked my chicken in grease where they'd just grilled some peppers.

As a result, I don't dare use spray. I figure that if I have to shoot somebody, I can cite that allergy to spray to explain why I didn't use that instead.

Sometimes a knife works, even if you don't use it. This summer, my maid was accosted by a man while walking home from a bus stop. She pulled a Gerber lockblade knife that I'd given her two days before, and her attacker saw that sharp blade and went back to his truck and left.