Well, either Steve misunderstood or I did. A wall 12" or so thick and only 12" high is going to be plenty stable all on its own. The surcharge (the force from the soil behind it) is going to be negligible. Just lay your rocks so they fit together fairly well and that's it. If you want to stop soil from filtering through the gaps , and stop weed growth , you can lay the rock on mulch cloth, tarpaper, or similar material, and wrap it up behind the rock to line the inside of the wall before you backfill with soil.