retaining wall and fence: how, and who?

We need to get a wooden retaining wall and fence replaced, and I could use advice and recommendations, either for specific contractors (the recommendations in the archive are fairly old), or for what the work should entail. The retaining wall is about 4 feet high, plus there is a fence and an arbor along the top of the wall.   I had two different contractors look at the wall, and they recommended very different things, and at very different prices.   One person is proposing ground posts, "buried 36" deep, in concrete, about 4 feet apart".     The other person is proposing anchoring the wall 'laterally', by means of rebar that would be attached to a concrete slab they'd install a few feet uphill from the wall. (Both are proposing installing a French drain, so that part is similar.)     36" deep doesn't sound like a lot to me for something that is supposed to hold back 4 feet worth of hillside, plus a fence and arbor, but I don't know what is necessary or recommended.  I'd be grateful for advice or recommendations.