This would cost ya about $160, and be really heavy, but your wheels would be armored...
http://www.google.com/products/catalog?q=round+shield&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&tbm=shop&cid=2332568729796513551&sa=X&ei=pqLyTbnlEoW4tge8o4SPBw&ved=0CIEBEPMCMBA