Render layers help!

My scene involves a character standing in grass, and I have a separate layer for both the character and the grass. Problem is, is when I combine the layers with Alpha over, the grass is totally overlapping the character, or vice versa. How do I get it to combine in an actual 3D space, so that the characters legs are IN the grass, not completely over or under the layer?

Ok, to get this to work you need to check the box that says “All Z” under each render layer so that it will take for acount the Z vaules of every face in the scene. Hope this helped.

Where is the ‘All Z’ check box? I can’t find it.

EDIT: Never mind, I found it! thank you so much!