Whether you're installing the footing for a deck, digging the trench for a retaining wall, or building a below-grade fire pit, you need to dig a hole with a bottom that is level and flat. If the terrain is also flat, the job requires nothing more than a shovel and a measuring tape. But on sloping ground, you also need a stake and a string level to help guide your digging. Here's how to do it.
1. Lay out the hole's perimeter, then begin digging at the lowest point until you reach your target depth, as measured from the low side of the slope. Continue digging the rest of the hole, doing your best to stay level with the target depth.
2. When most of the dirt is removed, drive a stake into the ground near the highest point, about 6 inches outside of the marked edge of the hole. Tie a string around the stake, hang the level on the string and pull it taut across the hole. Keep the bubble centered in the level's vial as you measure from the string down to the bottom of the hole at the low side. This string-to-bottom measurement is your guide for how deep to dig.
3. Take repeated measurements from the level string to every point in the bottom of the hole as you add, remove, and tamp the dirt. You're done digging when the distance from the string to the bottom is the same no matter where you hold the string over the hole.