Perhaps rather than a simple geo-fence, you have to physically trace an unlock pattern (visit a pre-determined set of locations in a specific order). The only

Perhaps rather than a simple geo-fence, you have to physically trace an unlock pattern (visit a pre-determined set of locations in a specific order). The only problem is that if you KNOW how to unlock the devices, you're required to unlock them. So really, you have to NOT know how to do the unlock (geo-fencing doesn't help--you'd be expected to tell them about the fence and how to pass). The point of the third-party 2FA is that you can tell them exactly what has to be done.