Minecraft wiki entry for Multiplayer_PvP_bases, associated text: Head to the nearest nether fortress and begin by walling off any corridors leading from the area you want your base to be. Then make sure any place you don't want blazes and skeletons spawning to have a light level of 15 (most easily done by covering the floor with jack-o-lanterns). It would be advisable to undergo obsidian padding. When you're done, move to the next step (after you've raided everything in the fort).