Instead of using a locked chest, require a unique banner to be created by the player, with the banner named the same as the outpost they wish to create. That banner pattern cannot then be registered for outposts by any other players. That named banner style should then be used for marking off the boundaries of the outpost and as an anchor for things like subplots etc.
Didn't want to include this as part of the main suggestion so as to create something for people to naysay then entire suggestion. Allow the player to also register a few (not every possible combination) look-alike banners as reserved - eg if their banner is red with a white per pale, they could register a white banner with red per pale inverted as reserved.
Banner patterns being 'registered' is something that would be VERY complicated. I don't see this being feasible.
Ok, at least use a "Named" banner as the basis. Allow people to do their own thing with the actual picture.
