Bah, someone beat me to it. I was gonna recommend this too!

I don't own one though so I can't vouch for it. Just gotta admit the dual utility(self defense, rain defense) of it seems more viable than other options.

HOWEVER the following is a VERY GOOD recommendation off their site:

“Our FMA training teaches us to be able to use items from everyday life. An umbrella obviously resembles a stick, but the simple fact is that all the umbrellas we've seen are too flimsy for most serious purposes. THIS ONE MEASURES UP. To confirm the claims made at http://www.self-defense.info/umbrella1.html I have put it through full power two-handed baseball bat swings at a heavy bag (I didn't bother to stand on mine though). The impact generated was impressive and the umbrella still readily opened with the push of a buttton. We think this umbrella measures up as a worthy self-defense tool--and as an umbrella too. Woof!”
—Crafty Dog (Marc Denny)


Marc Denny is a VERY well respected filipino martial arts instructor (which I am a long-time student of - see my title?). The guy KNOWS what he's doing and regularly tests it in a live sparring situation (full contact stick fighting).

That just sold me. I want this umbrella.