Hmmm guys, we are in trouble!
I'll try to figure out, but it will be hard (working sort of blind here).
About the second plane (or planete or whatever object) trick... If I have two planes I don't need to merge my textures. It's just a little solution to a specific problem with the merge shader. I don't even know if this problem still exist on TG3.
On TG2, WHEN (and only when) I have artefacts with the merge shader, I thinking like this: sand = water, problem solved! So I make a "lake" of sand, and it's solve my problem. It's not elegant, it's a cheat, but it work (typical example: sand dune on bottom of a martian crater).
Now, if you want to distribute some sand in your scene, TheBadger is right, you need a distribution shader (or a surface shader) to place it in the scene.