Hi George 4 steps up probably represents 24 to 30 inches...yes? The main issue here is digging your footings for your retaining wall down to the frost line and making sure the soil/sand in the raised patio is well drained. It is the collection and holding of water and its subsequent freezing that causes the expansion problems we all see. There is no practical retaining wall material in existance (that I know of) that will withstand the expansion of frozen water...so the trick is to make sure the water flows away. In your case, drainage tubes place around the wall at various levels should prevent water build up behind the wall.