Where to put distribution shader for rocks?

[yesmine]

I'm experimenting with a scene having a low rocky/sandy terrain containing 2-3 different sizes of rocks. A sand shader is plugged into the Input node of the Surface Layer, and the rocks are all merged and plugged into the child node input on my Surface Shader, and it all seems to look fine. The sand shader is .tgc clip I found that already has a distribution function in it, which conveniently gives me control over the sand altitude/slope. However...

I've been searching for a way to insert a Distribution shader to have altitude/slope control over the rocks as well. The Wiki on the Distribution shader gives an example of plugging it into the input of a Populations density shader, but I'm not using a population per se, and none of the Fake Rock shaders or their Merge shaders seem to have a density input.

Is it possible to insert a Distribution shader to control Fake Stones shaders, and if so, into what input would it need to be plugged? Then, can one distribution shader be hooked to all the rock shaders to control all of them at once?
Thanks...

[fleetwood]

For Altitude and slope you don't need any thing but the Surface Shader. Look at all the tabs inside it. It has inside its own Altitude and Slope settings.
Fake Stones shaders have a Mask Shader input. You can plug various Shaders there to control placement.

[yesmine]

Thanks for the info. I know the surface shader has built-in altitude and slope controls, but my take on that was that it would end up controlling everything coming through the surface shader. Maybe that's mistaken on my part, but I'd like to control the things before the all converge in the surface shader. I have that with the sand clip, since it has the altitude/slope controls in it (like the surface shader node has), so what to do with the rocks..?

I'll look into the Mask input as you suggested, but a Distribution shader would do the trick for now..if I can get it to work.
Thanks again..

[fleetwood]

I think that after a few experiments with it you will have a different "take" on the surface shader. 
The surface layer's altitude and slope settings apply to the individual layer,  not everything above the layer. Try turning on the test color to easily see where your surface layer shows and where it doesn't.