Backyard retaining walls

All this rain has been reeking havoc on our sandy backyard. It's beginning to cave in on itself. 

We were always planning on building retaining walls for the area we previously dug out, but we were hoping to do it later on as part of a whole backyard plan. Unfortunately, we can't leave it very much longer, so I got the guys to work on it today.

The south side of the house will be our entrance to the backyard, so we want to do it up nicely.  The north side, though, will eventually be hidden by a deck.  So over there, we are really only concerned about function. The cheapest way to go?  For us it's rebar reinforced cinder block on a 3 ft concrete foundation. It's not the prettiest retaining wall ever built, but it will do the job.

We have our stone guy (so fun to have a stone guy!) coming in later this week to give us an estimate for the  south side stairs and retaining walls.  These will be built with the old foundation stone that I rescued from the dumpster.  He's as excited about re-using that old stone as I am.  Actually, I think he's even more excited.  In fact, I don't think I've ever met anyone as excited about stone as this guy.  And wait 'till you see what he does with it!