Is there ANY place safe to keep cash?

That's a good spot. 🕳️
But wrap the packets of bills in aluminum foil 💵

Carbon paper is actually better. The little strips now embedded in bills as an identifier emit a tiny magnetic signal. When there are enough bills involved those signals can be detected. Carbon paper blocks that. Border Patrol uses the technology to halt drug cash flowing south to the cartels. Don't ask how I know but it's a FACT.