Things You'll Need
Instructions
Place a dispenser anywhere on the map that needs to be protected, facing the direction from which monsters are most likely to approach.
Right-click the dispenser and add arrows to the inventory window that pops up. While many items can be launched from a dispenser, arrows cause significantly more damage than non-threatening objects, such as snowballs or eggs.
Place a pressure plate in front of the dispenser. The closer the plate is to the dispenser, the harder-hitting the arrows will be.
Drop red dust on the ground between the dispenser and the pressure plate to connect them. Red dust acts as wiring in "Minecraft," so depressing the plate will launch arrows at whatever is weighing it down.