Use a real strong magnet, hard drive magnet or a microwave magnet.
In NZ the scrapmetal dealers give out free keychain magnets with their website address on it.
The amount of metal I have gotten simply because I had the magnet there at the time... a few thousand $ more than the keychain ever cost..
Impresses people too, when I pull it out, they KNOW I KNOW the business....
These sorts of keychains. (
http://www.magnetcompanyonline.com/) 7cents each!!!!!
http://www.magnetcompanyonline.com/images/sm/bigboy.jpg