[howmayiannoyyou]

Better off with a strong shallow field, high intensity rare earth magnet attenuated by a removable stainless steel shield that erases the data only if the USB key is removed from a holster incorrectly, thereby removing the stainless steel shield.

[LeifCarrotson]

It's a USB key, not a floppy. Magnets do not affect Flash storage. Typical (austentic) stainless steels do not attenuate magnetic flux.