What can i put on metal so magnets won't stick to it?

I have an obnoxious coworker who insists on hanging his sports team magnet in my work area. The specific area is about 1 foot square, very thin sheet metal. I don't want to take or destroy the magnet - I'm not that kind of person! -- I just want to fix it so he can't hang it in this particular area. Is there a spray adhesive or something more permanent than tape that would remove or reduce the ability of the magnet to stick to it? The metal is nothing showy, I'm not concerned at all about scratching or damaging it - it's in a rough environment already. Any help would be GREATLY appreciated!