Love these kinds of problems.

I've always felt for very critical equipment you'd be better off designing a PCB to be physically cracked in two, such that you need both specific halves for it to operate at all, and then ship each half separately. E.g. the electronics version of tearing a dollar bill in half and matching the two halves to verify the identity of the holder (something I've seen in spy movies). You'd probably want to make sure the recipient got the first part before shipping the second, just to make sure.