A wall of stacked stones.
Check with your community's building department before setting out to build a retaining wall. Many codes require a permit for any structure that holds back what amounts to thousands of pounds of earth, and most limit the height of an amateur-built retaining wall to 3 feet. If your slope needs a higher wall or requires extensive grading, call in a masonry or landscape contractor -- or terrace the slope with two or more lower retaining walls.
This loose-stone wall is built with ashlar stone; other, less-regular cuts work equally well, although you might want to tip the wall farther back into the slope for stability, and, for looks, fill gaps between stones with plantings.
Loose-masonry retaining walls don't need a drain system as other types of walls might, because they drain naturally through chinks between the stones.
1. Lay out the wall with stakes and string, then dig a shallow trench, cutting its back side at a slight angle to the slope. For drainage, lay about an inch of gravel in the trench. Our wall will turn a corner, but the same techniques apply to straight walls.
2. Lay your longest stones on the bottom; the fewer the joints in the first layer, the less frost will heave it. As you lay stones, level them as best you can by tapping with the handle end of a sledge. (To prevent possible injury, use your legs, not your back, to lift heavy stones.)
4. Dig a hole into the slope every 4 to 6 feet and lay a long stone crosswise to the wall. Pressure from earth above these stones will tie the wall to the soil behind it. Finish laying the stones, then backfill as necessary.