[A Cobra guy]

Forget the magnet idea.
A magnet will permanantly lose its magnetism when heated. There may be some very strong ones that won't do this but I'm not sure. I used to sell science supplies to elementary schools. we would bake small magnets to get them to lose there magenism. As I recall it didn't take much (350 degrees for an hour or 2) The kids would be given to things that looked the same but one was magnetic and the other was not.