Another way to build a pretty good wall is to use regular concrete block with a rough cut appearance on one face. As you set them, drop a piece of rebar into every other hole or so and pour all of them full of concrete as you go up. To be safe, put layers of perforated plastic pipe surrounded by gravel immediately behind the wall with silt screen separating the gravel from the dirt behind it. That way any water that might cause frost damage will be able to drain away. I do something similar, but instead of block I use barnstones -- pieces of sandstone about 2 x 2 x 3 or 4 feet. They don't move much if properly installed, so they just sit there without the rebar or concrete.
