Minecraft wiki entry for Player_versus_Player, associated text: Players in diamond armor might come and kill you and raid your chests. You are in iron, huh? Shovels are your weapon here. Put snow blocks as the one layer floor block, dig all the way to bedrock, (or the void if in The End/custom map with no bedrock) lay TNT everywhere (just make sure it is out of reach from your base), and depending on how strong they are or how much you hate your enemy, put a manual switch or lay tripwire to automatically blow them up. Note that you might not get their loot.