Regarding the issue of aggressive dogs on the street, for years I've carried a cane while walking my small dog. I recommend it to anyone walking about, since there is no telling when a hostile dog will show.
I recently met a retired policeman with a martial arts studio in Galt where he teaches something called "Cane-Fu." Besides being a legal defensive strategy for any law-abiding citizen, it's also a method for getting into shape. It's supposed to be especially useful for the elderly, since its focus is on aided stretching and low-impact workouts.