...and keep removing it. Leaving it up only invites more vandalism. Graffiti taggers will eventually give up trying to tag a particular surface if their "art" constantly and quickly disappears. If acquiring paint and materials is a problem, I believe C.L.I.P. or the Anti-Graffiti network is will to provide a voucher.

Don't worry about some idiotic tagger shooting you. They are cowardly worms who will quickly back down if confronted. Their petty crime nets them no profit and they do their dirt under cover because they're too yellow-bellied to face anyone.