Paint Problem - Need Help...

My school, NCSU, has a freedom expression tunnel, seen below.

As a member of student senate, we need to make the tunnels safer at night.  Students paint on the plastic coverings of the light reducing visibility in the tunnel.  Since a rule against painting parts of the "free expression" tunnel would neither be practical nor enforceable, is there some way to prevent paint from adhering to the light coverings?

Periodic cleaning of light fixtures is proving inmpractical, since people of our ~40,000 student school paint part or all of the tunnel every night.

Thank you for your ideas.