I've seen some pretty solid looking pumps that could be defensive. You would probably break the pump, but safety is worth it.
I carry my Ulock in the net pocketing on my backpack, If I really needed to defend myself I would have a VERY heavy oversized piece of metal to do such, but I think the best defense is to go fast.
If you know a "bad" area is coming up just peddle fast. Your drivetrain will be quieter (I think that might agitate dogs)
(is C - H - U - N - K really censored? Really?!?!)