This is a decent one. I used hydraulic cement when I did mine but the marco mortar is about the same thing.
http://www.3reef.com/forums/live-rock/creating-rockscapes-using-hydraulic-cement-106335.html">http://www.3reef.com/forums/live-rock/creating-rockscapes-using-hydraulic-cement-106335.html</a>
When I do mine I let it sit for about two hours then I set the rocks in water with a powerhead for about 2-3 days.
