Its rather annoying

I keep flipping back and forth between RTO on and off.
RTO (Ray trace objects) on and the forest and grasses look fantastic but the Rock Object wont displace.
RTO off and the forest looks cr@p and the Rock Object looks great.
The shadow casting from the Rock Object (RTO off) is odd and wont comp well with the trees and grasses (RTO on).
Round and round I go. I tried Dunes suggestion (thank you) of using a Fake stone shader, it kinda works but makes a different "style" of stone which if its in the wrong place (it will be) needs to be "transformed" to the right location. This causes a shear in the stones displacement.

Its looking like my best chance is to go back to where I started and make a physical model of a stone, maybe in ZBrush or similar.
Still its rendering away at the moment (RTO on) and I'll see where I go from here later this evening.
Richard