This would be a Booby Trap and is illegal, so it's not worth it for that chance of going to prison no matter the value in the safe, if you are a billionaire. It would be hard to find someone willing to help you.

Is it still a booby trap if the safe displays a prominent warning, "CAUTION: EMITS DEADLY GAS WHEN DAMAGED"?

Depends on your lawyer.

The law is someone less picky about armed guards, though, so you may just want to pay some thugs to watch your safe.

Gandalf - “But men are better than gates, and no gate will endure against our Enemy if men desert it.”