Side note, but I've thought about this and wondered the same thing. Where do you keep 500M? In your house on an offline hard disk that can be stolen? In a safe deposit box? This is a true data backup scenario where too few copies and you're in trouble and too many and you're in trouble. Especially since a copy that was found without your knowledge could ruin things before you knew.

In your head. Or rather, you encrypt all your super secret private data with a good password that you never write down, and copy the encrypted archive everywhere.

And then promptly forget it when restoring from backup in ten years.

This assumes your encryption scheme is perfect and will be for the life of the secret. With 500MM it would take you a minute to move or spend it so you have to protect against someone getting the secret and being able to break it in 10 years or whatever.

Its an interesting problem. Paper wallets can be encrypted with a password, which is one step. Using multi-sig is another. Having canary addresses is yet another way. Of course in this case not all of those are an option since the goal seems to be to not move them at all.

You split it with Shamir's Secret Sharing Scheme, print the pieces on multiple sheets of paper and store them in various bank vaults around the world.

But have too few redundant copies and you lost access to it forever. Or travel to various countries opening bank vault accounts is sure to put you on CIA/NSA/othersuchagencies' radar. $500M is interesting enough for them to poke around I bet.

Or of you loose access to a country for some other reason you're screwed as well. Also, if you're otherwise not well of spending 10+ thousand to land the secrets in several countries is not an option either

I agree. Once he said "In the next few days i will move a coin," he told every savvy crook in Australia "follow me around for the next few days"

EDIT: this is presupposing he's not a con-artist, which is still my hypothesis