That’s possible as long as the police aren’t robot, and the mansion isn’t orbiting in space. Now Elysium doesn’t have to happen (and good luck with the giant space station) but a sufficiently walled garden guarded by sufficiently automated defences supplied by a sufficiently automated workforce could in fact repel anyone else trying to get in with nothing more than small arms.
Though I reckon an organised unwashed mass could most likely do something.
I see the reasoning but in practice it’s just sci-fi I believe. Even if you have the _perfect_ walled garden… there you are with your wealth. What will you do with it if everyone else refuses to deal with you? What are shares of corporations worth if no one cares that you own something? Why would the military listen to you, when they could obliterate your escape room and take over your wealth directly?
All this stuff you mention relies on the the „fact“ that capitalism and guaranteed private property rights are absolute truths - when in fact they aren’t, actually more like a temporal fashion wave in some parts of the world, and faith in this destructive obsession in „the economy“ is on the decline finally. :-)
Though I reckon an organised unwashed mass could most likely do something.