Figure C--If you are adding a retaining wall, make sure the area is level throughout the process. A two-inch-thick bed of concrete serves as a good bed for the cement blocks. Be sure to wet the blocks down as you lay them so that the moisture from the concrete bed doesn't wick up into the cement.
Figure D--Cap blocks are the best way to cover the holes of the cement blocks and provide a smooth, clean look to the wall. You may choose, however, to fill the holes with soil and use the blocks as planters. You can also choose from many decorative stones to serve as cap stones.