one of the problems might involve that you are to close to one of the main towns (spawn, northtown, southtown, easttown, or westtown) another problem might be that you are in someone's protection stone thus you cannot build there either. my suggestion is that you look at the live map on this web site, find a place that isn't to close to one of the towns write the coordinates down and head there to build or take a long walk out somewhere until you find something

i think the simplest solution is that only trusted and/or moderators can move them from on place to another. this will keep anyone just randomly moving them places and the trusted or moderators can keep track on where what is to a better degree.