I am pretty sure that a court could order your backyard to be excavated if it believed something important buried there.

That said, hiding evidence from law enforcement/money from the tax authorities is a crime anyways, regardless of where you hide it.

Warrants cover everything in the U.S. I'm referring more to people that shove their money into offshore accounts designed to be hard to locate and examine. Think the cayman islands, the panama papers, etc. Physical money already has to be declared if over a threshold and moved across borders, and I don't have a problem with any amount of cash kept wherever locally. If it's illegal in some way there are methods to find it.

The goal isn't to lock all money down and infringe on personal rights, it's to keep it from being hidden and untaxed en masse by many very rich entities.