For surprise of tool used the saw vs safe are the best:
The main thing locks do is make it noisy to get in.
The main thing locks do is make it noisy to get in.
A hardened metal safe designed to be resistant to cutting can still be cut through, just not in seconds with a screamer saw (trade name for a metal cutting circular saw)
If you want truly secure, encase your metal box in concrete like John Wick. Access is difficult but security is high :)
FYI, most safes already have a decently thick concrete layer — that’s most of why safes are heavy! (Or, I guess you could say, adding a concrete layer is cheaper than making the steel thicker.)
But they also have a rubber or foam (often styrofoam in cheaper safes) layer, to “smooth out” the force from a sledgehammer, jackhammer, or just dropping the thing out the window.
And a layer of compressible wet(!) sand, to spread out the point stress from a hammer and chisel, impact gun, gunshot, or small explosive configured for concussive force. (The goal here is essentially to replicate the behavior of a bulletproof vest.)
Plus, they often contain a layer to bind and foul and dull (or even break) the teeth of drill bits and reciprocating/chain/band saws. This can be any number of things — low-melting-point plastics, recycled broken glass, etc — but look up “proteus” for a fun read.
If the safe’s designer is clever, just a few materials can serve several of these functions at once. But more is always better. Which is why good safes (and vaults) are so dang thick. It’s not to solve one problem really well; it’s to mitigate N problems acceptably well, for a frighteningly large value of N.
In an analog to the somewhat frequent observation on HN that if you don't care whether the code is correct I can make it run arbitrarily quickly, if you don't care if the contents of the safe survive there's a lot of high-energy ways to blast it to smithereens. This is generally not considered a problem to be solved with a safe, though. If you want to prevent "being blasted to smithereens" that you'll need a completely different approach.
The law is someone less picky about armed guards, though, so you may just want to pay some thugs to watch your safe.