I suggest using the db to store player coordinates when they logout/disconnect (teleporting player to spawn afterwards), and tp them where they were after logging in - that way, the chances that client gets the coordinates someones at without logging in (before they are teleported) become zero. I didn't really see anyone use this trick to get hidden base coords, but it doesn't mean it's impossible.
Also, hiding player inventory on login could be a nice feature (but, that'd require a way to store it in the db).
Also, hiding player inventory on login could be a nice feature (but, that'd require a way to store it in the db).