Underground safe and hidden stashes with the guns literally buried.
Have a few gravel piles on your property with empty boxes buried for a decoy under them.
Then get some water tight containers and some bricks and submerge your weapons in a small pond / lake...
Grace, if the gubmint goons are busy confiscating guns, it's time to use them for their intended purpose - not hide them.
How about just use the guns instead of hiding them. If you don’t, you will probably end up dead anyway.