When we were allowing foreign items into the area, he built (and later destroyed) one of the best hideouts out there!
Took me days to find the entrance to his system of lookouts, caves and farms and he operated just outside of the safe-zone gates..
Was that the one we found and spent ages putting levers everywhere because we were convinced the blank wall must have been some secret thing - but never found anything lol
... and then used the treehouse as a giant diving board?
I don't bother hiding things. I think you can count on one hand the number of incidents we have had on our servers over the years. It's a good place to play and people are generally respectful of each other and genuinely just want to build their stuff and see what awesome stuff other people build.
I was contemplating hiding all my machinery behind some sort of elaborate piston-wizardry - just because I thought it would be cool to press a button and have a wall drop down with all the industrial stuff behind it, like some sort of hidden lab inside your house.... but I'm not good enough with the redstone to be able to do something like that (one day I'll figure it all out)