Entrench

You create a fortified, entrenched area. The area consists of up to six 5-foot cubes which must be connected to each other on at least once side, and the tops of which must be level with the surface of the ground. It can bend and twist as you desire, but must fall within these overall size restrictions. It takes 5 feet of movement to enter the trench, and creatures who enter the trench receive the benefit of full cover while prone, or 3/4s while standing.