Two fog color in the same scene

In my game I have a curvy plane that separates the scene in half, like so:

I would like to add some fog to add some athmospere, however a single color wont work, as the top part should fade to black, the bottom part to white.
I tried to achive the desired effect with two cameras, witch kind of worked, but since the ground has that curve in it I cant really tell the rendering order of the objects (somtimes the plane should cover the boxes, sometimes the boxes should cover the curve, etc)…

Any idea what sould be used here? Is there a way for the two cameras to use the same depth-buffer, so objects beeing farther gets covered by closer ones regardless of the camera that rendered them?

For anyone interested I solved it by using a custom fog-like shader with different properties on top and different on bottom.

@Ripityom Im not sure how similar of an effect im going for is to the one you have here but in my game im trying to have one camera render above the water and one camera render below the water plane. The water plane is using a vertex displacement shader to give it the water feel, but i cant figure out how to tell one camera to render only above the plane and the other to only render under the plane. My goal is to have different fog settings underneath the water and separate fog settings above the water plane.