first set of rocks dry fit
 

It looks like I will need to have 3 sets of rocks. Here is the first nearly done. I decided that I wanted more of a platform so I put my "mountain" type rock on the side and added a few more rocks. This is where I added rocks.
http://i10.photobucket.com/albums/a1...psrhtgzbgg.jpg
Notice the "potato" like rocks. They are just tightly wadded newspaper with fiberglass over them. Easy to make. Behind that large triangular rock is a hide for the fish.

This is the dry fit of this one part. It dosent look bad. It is now a dark gray color. I am a bit wary of the color because it looks like cement. I may go more red/ocher. Not sure. Any way, I consider this a base coat any way.
http://i10.photobucket.com/albums/a1...psi5uxzqxd.jpg

The water level for the fish stops at about where the bottom of that ledge is. The top of that ledge will hold some masdevalias and dripping selginella.
Another view.
http://i10.photobucket.com/albums/a1...psv0whepum.jpg

On this section I still have to plumb it square and finish the edges as well as complete the color and texture.

Nice, such an undertaking. What do you put over top of the rocks?

Auto body filler. I mixed it with Mars Black and Ocher color acrylics, then used the catalist. I layered it on by hand, sort of finger painting with gloved of course, and burnished it with sticks, did some top sanding with fine grit sand paper. I will eventually put a clear top coat of some Kind as well.
http://i10.photobucket.com/albums/a1...pssibin6pp.jpg

Hummmm clearly not toxic to fish then.

Apparently fiberglass is used for tank backgrounds all the time. They even sell them. Auto-body filler is fiberglass resin with talc in it. Strangely, some people even make fiberglass fish tanks. DYI. You can usually just see out the front. They can get huge, like 2000 gallons. Tanks, backgrounds, and so on are made all the time by folks like us. As for the paints, I chose only earth element colors. Mars black is made from chared bone, and ocher is from earth clays. I would not use blue or green (etc) because they do contain toxic metals.

See there is so much I don't know. Keep up the good work.

I totally understand. I have been obsessing on "how" to build this back ground for more than a year.