As you might be able to see from the photo the soil is a heavy clay however to excavate the area for the slab I needed to go down to rock. This means to put footings in for a bock retaining wall I would need to get a rock breaker back in for a number of hours to dig /chisel down any further in the rock. I have however thought about running more reinforcing along the slap and up at right angles to increase strength.Height ranges from 400 to 800 on the slopeHowever I am now considering a building a retaining wall using CCA treated pine sleepers 200 x 75, and using the new stumps (which go down a further 600mm into solid rock in a concrete footing) as supports. Obviously I need to dig out more of the soil to put in drainage and backfull but I donít need to dig down any further. I am also looking at putting a channel drain at the top as well, lining the wall with plastic sheeting doubled over. My concerns, the spacing between the stumps means I might need to put in more posts for a timber wall, however the soil is clay / down to rock in places so I am not sure how much movement there will be. How long to the CCA sleepers rot out and I end up having to dig it all up to replace them?Another option suggested was to frame up the stumps, put in a load of reinforcing steel coming up from the slab, a few seep holes and pour concrete in and make a concrete retaining wall with a few stumps in it.