If dogs on the MUP is what you're worried about, I would think a good hard kick would suffice. A kick to the owner might be a good idea too.
When I lived in Queens there was a huge Akita that on two-occassions broke through a closed car window to attack another dog. The dumba@@ owner thought that was cool. Whenever that dog was around I made sure I had a knife in my pocket to cut its throat if it ever clamped onto me, my wife, or my dog (or anyone besides its owner).
See what your local postman carries, and ask him if it works. If he's a walker, chances are he's had to use it.
As far as bears -- the black bears that may stumble into your area will be much less of a threat than any dog, and can be scared away with some loud noise.