Minecraft wiki entry for Defense, associated text: 1 pressure plate (Preferably stone, as things such as drops from burning mobs can activate wooden pressure plates.)
1 powered rail
2 or more minecart with TNT (If you use more than 2, the explosion will do more damage.)
1 block (Choose a block that matches the rest of the ground on which the mine will be made on/in.)
1 rail (You will get it back once you are done.)