Minecraft wiki entry for Defense, associated text: To make a TNT SDS, first dig 3 blocks under your base. Fill it with TNT on 3 blocks under your base. On top of the TNTs, put your normal blocks. On top of that, fill the 3rd floor with redstone. Now put repeaters on the 3rd floor (right-bottom of the real base's floor) and make a road to where you want activator be. Put a lever in the activating zone, and connect your SDS to the lever lever using redstone and repeaters. When your base is in danger and lots of enemies in your base, take as much loot of yours as you can and run. When you are near the Activating Zone, you can now pull the lever and kill all the enemies. One SDS looks like this: