20 NdFeB magnets should do it
They are AMAZING!
(Maximinimusyou stick around I'll make it worth your while, Fri 3 Jul 2009, 16:49,
archived)
I only invest in them when they're at least 15 years old
when they've proved they can stand the test of time
(Grrrmachinethe indifference engine, Fri 3 Jul 2009, 16:51,
archived)