ZBrushCentral

How to sculpt 2 layers independently?

I have a question involving using 2 seperate layers that I would like to sculpt indepently. I have one mesh/tool that is a layer of rocks, and a second mesh/tool that is a layer of dirt. Is it possible to someone combine the 2 on canvas and say selectively sculpt only areas on the dirt layer to raise/lower parts of it to cover certain rocks? I believe I can get a somewhat similar effect by placing the rock tool on a 2.5d canvas, then the dirt layer and moving it closer/further away from the camera but I was looking for a way to raise only parts of the dirt rather than the entire layer. Thanks! And yes, I am a super nub.

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Can you post a screen grab of your subtool palette with the 2 meshes.