Have you tried wrapping it in baking foil ? Like brass and lead it won't stop static magnetic fields but it will minimise induced currents from variable fields (body scanners, electric motors etc)
Have you ever tried watching a compass whilst on the tube. You'd be amazed at the varying field as the motors are switched. Yes, it takes a sad person to "discover" that effect. Just happened to wonder what direction we were heading in and my compass was swinging all over the place, even when the train wasn't changing direction.
jack