I don't know yet where this goes. I have spent some time to give the stone bed some attention, and am very happy with it.
The hero rock came out because at first, i tried to add another surface layer on top of the stone bed to add bigger rocks. That however screwed up the underlying fake stone bed entirely and I haven't been able to find a cure. <insert heavy swearing here>
Then I thought "why not try a sphere?", and that got me into doodling mode ;-)
I'm not sure the sphere is a good idea for hero rocks. It doesn't seem to accept displacements from a power fractal, but it accepts displacements from the displacement port of a surface shader, which - unfortunately - can only be controlled through color.
Not sure yet, but I believe I let go of the "hero sphere" concept.
Funny how this developed, I really wanted to perfect the stone bed, and then got crazy on trying other stuff. At first, I tried to cover the stone bed with thick snow, but that too screwed up the stones totally - Damn, I was angry that I couldn't figure this out.
Maybe someone else had succes with adding thick snow on top of a stone bed?
Cheers,
Frank