most of these places are too well known, they get into the newspapers on a"low news" day and everyone can see the pictures for themselves, they may be fortified and indeed safe, but they'll end up as someone tomb if they don't watch out.
being big and bold and thinking you need a fort is not the way to go...discretion and a good plan is way better.....that grounds keeper in his old clothes is one of those highly trained bodyguards.....the guy cleaning out the small barn and taking care of a few sheep is also one....that old barn also has a hidden gun/ammo locker...If you make yourself a target you will be one.....
That is the same line of reasoning as the "Gray Man Theory"
I like to question and look at things from many angles.....even if I had millions I would not buy or build something and be foolish enough to think I was good for whatever happened.....I would have several plans and hideaways in place......