Last time, we said you’d need a deadman to finish off your retaining wall. Relax, a deadman is simply a length of timber which extends back into the hill, where it’s braced by a bar or additional timber. This helps hold the wall against the hillside, so it stays straight and sturdy for years.
You’ve already dug back into the hillside. Lay your deadmen in these trenches, resting on top of the previous course in the wall. Drill a hole through the wall-end of the deadman, penetrating at least two other timbers, and insert a pipe or rebar in the hole. On the other end, drill another hole and drive a rebar. A perpendicular section of timber below the deadman at this end adds even more stability.
Lay the other timbers in the course, so they butt up against the deadman, and continue your courses as you have so far, using pipes or rebars to lock a number of courses together.
Lay a drainage pipe, perforated at the upper hill-facing side, in a bed of gravel along the back of the wall. Cover the pipe with drainrock, and backfill the trench as you build.