Making 2d orthogrpahic scenes without seams

My problem is this:

I am making a level for a 2d game, and I want to have a foreground and background and then a sky. The forground is what you walk on, the background is things like trees and waterfalls and things, and the sky is the sky.

I want to have the forground as one object and the background as other ones, on two different layers, but my terrain is all one object, and it goes from the background into the forground. My problem I get then is I need to seperate the background from the forground, which prodeuces this seam:

The object on the right is the background and the object on the left is the forground, were the person walks.

Thank you for any help.

I need a better viewing angle of your scene.