Re: tamper-proof screws aren't
There are such things as tamper-proof screws. They are countersunk (of course) and made of some hardened steel, use-once and done up with a standard crosshead screwdriver. However the head profile is sort of sloped so there is no 'undo' edge. The really sneaky bit is the underside of the countersink has lots of reverse sawteeth. They slightly deform the underlying metal as you screw them in, and even without the odd head profile, would dig in hard if you tried to undo them.