I start with a wide solid base and just work my way up, no glue.
It takes me a long time, this time was about 2 hours. The rocks are not supported in the back in anyway, I think 1 might be touching but I really try not to have the rocks touch the glass. I do have egg crate on the bottom though. Trust me I have been looking for the secret of rock piling and have yet to find one. The best advice I can give you is have patience!
I will go takes some side shots now.

I will go takes some side shots now.