Thanks for the info everyone. After doing a bit of research regarding the use of Hydraulic cement, I think I am going to go that route.
As I won't be ready for set up till late next month some time, I have time to build my rock scape and cure it.
As I won't be needing too much ( my rocks are pretty large, I plan on using PVC pipe ( with holes drilled in it to help minimize stagnant water ) to help hold the structure together and use the Hydraulic cement to fill in the gaps as well as add a bit of adhesion.
Does anyone have experience with the Quikrete brand Hyd Cement? Pro's and Con's, aside from the initial PH spike?