Overwriting depth texture with "obscured" geometry

[thick moon]

I'm using a simple hole shader to render trenches/craters below the flat ground plane. However, these holes do not affect the depth texture for post-processing effects (fog, ambient occlusion, etc.). Is there any easy way to get the lower geometry to overwrite the depth texture?

here's how it should look except for the missing ground

[kind imp]

I don't know if it's controllable in unity somewhere, but on the graphics api level, you can set the depth test/write action as overwrite. Then it should work as long as the trench is rendered after the ground.

Probably you can set that in shaderlab