So, every day I get X-Rayed by someone, and they instantly find me out and say out loud in chat. I used to use hacked clients (I don't use them anymore, don't go mental .-.), and I know that sometimes X-Ray is not configurable. It can see through practically everything but ores, so you could make (inside of walls) diamond/emerald ore. That way, when they try to look through, they see a wall of ore. This would only partially work on maps other than ones in halls, such as office. Ones like Oasis would be a lot tougher, but could be used between the ground and the tunnels. It might not solve all cases of X-Rayers, but it would definitely help out with a notable portion of them.