Minecraft wiki entry for Multiplayer_PvP_bases, associated text: To make it easier, build murder holes (holes in the floor or ceiling that you can shoot arrows though). You may also want to build a few "outposts" around 50 blocks from the ground. That way, you can kill enemies easily. Beware though; if you build outposts, then it's a dead giveaway that there is a sky base somewhere around, so only build them if you have at least 2 chunks of land in each direction claimed and aren't worried about stealth.