I agree -- great job. I would not put them on the bottom. Put a few big rocks like the one in the pic on bottom and then set the condos on them about 1 foot off bottom in and in about 4-5 ft of water. Wire them to the rock to keep it in one place and sturdy. You can also tie them to a pole and drive the pole into the bottom. See below.

http://www.sdafs.org/reservoir/manuals/habitat/spawnpip.htm

http://www.sdafs.org/reservoir/manuals/habitat/Main.htm