Minecraft wiki entry for Survival_in_an_infinite_desert, associated text: A deeper trench is a killing trap. Lure hostile mobs towards you to get them to fall into it. Chase passive mobs away from you, into the trench. For weak mobs a trench with steps at each end is fine, so you can go in and out to collect loot. But for dangerous mobs who might survive, leave the ends sheer drops, and build stairs down after all mobs are dead.