To begin trench composting, choose a location in your garden that is free from roots and underground utilities. Building a trench that is about 0.8 to 1.8 meters deep and 3 to 30 meters wide, depending on how much compostable material you have. You can also build multiple trenches if you have a large amount of sheep material. Next, fill the trench with a mixture of your sheep manure. You can also add small amounts of shredded paper and straw, sawdust, and eggshells.