A friend of mine has about 40 feet of fence backing on an alley. He got tired of idiots lurking back there and spraying up his fence, (plus one moron sprayed paint through the fence at his dog). We decided to get even.
When the little jerks came back for another round of scribbling, we snuck around the alley and fired them up with paintball guns at close range (can you say headshot).....
I think he kicked them a few times too. Word got out that some crazy dude lives in that house, and now magically no more grafitti... (BTW his first suggestion was to use a Nail gun and tack their nads to the fence.)