Minecraft wiki entry for Guardian_farming, associated text: One of them is the iron golem method, where guardians spawn and are funneled using water currents to a trench filled with iron golems. As the iron golems attack the guardians, the drops are collected using hoppers and deposited in chests. This method is fairly iron-heavy, due to all of the iron golems, which will need to be periodically replaced due to the guardian's spike damage, and a large number of hoppers used.