I wonder if there should be a forum dedicated just to security...
I'm sure you're all familiar with

How to deter?
Idea 1) Steganography
Idea 2) Additional factor: Share the private key between 4 execs. 2 of the group are required to decrypt the code. 4 not 2 in case one of the pair dies.
Idea 3) Time based auth. Have a factor that only becomes clear when a certain time happens. Hard to implement in practice? Could it be something such as how light falls on the earth or something stranger? How could this work in practice?
Idea 4) p2p auth. Need a peer to peer network agree and get concensus to decrypt the key.
Idea 5) Deniable encryption. Like carrying 2 wallets, one low value. Can't see this workingm they might be able to tell you are lying.
Idea 6) Do something funny with public key encryption?
Idea 7) Just bury half of the key somewhere awkward to get to. In another country perhaps. If you had a yacht and got captured would this deter or would you really want access to that for a bribe?
Anything else? How to make these things more workable? Is there a way to give a 3rd party access to a wallet in such a way that they can only pay out to an address you hold? That way you could give grandma/wife half the savings and get an allowance so you can't go gambling.