Glad the magnets helped... for awhile
(been there, haha)
seifrob's idea sounds good- how about some, say, 3M body tape they use for automotive trim and the like? That way it'll be semi-permanent while still (hopefully) being buff-out-able.
Also, check Craigslist for coroplast if you haven't already. A couple weeks ago I scored four 4x8' sheets for $30 total. Four! (And I didn't even get murdered)