Some more concepts:
Trench with corners and blocks distributed at various distances, which allows some modulation of distance and angle so that all positions can be covered but no one position is heavily exposed. Block distribution also hampers both rush attacks and grenades.

Camo bunker - a LOT more time-consuming, terrain is almost never designed to do this; I had to add a lot of blocks to make the example work.



Trench and bunker designs are suited for pop-up sniping. Most of your time should be spent with your head DOWN, because that gives you the advantage of surprise:
Sniper: Down, down, down, down, shoot
Travelling Enemy: Nothing, nothing, nothing, nothing, dead
Short of building their own wall, trench or tunnel, the traveller is always at a disadvantage with pop-up designs. They can't anticipate until you fire(and even then, it takes time and good communication for a team to be alerted), so even if they're doing their best to scan all angles, they can only hope to get lucky.
On the other hand, when I see this:

It won't matter that it's the same color as you. I am going to be pointing towards it, and I will see your face appear. It only works in your favor if you take the time to build a gigantic fortress, or you use it as the decoy and snipe from an entirely different angle; as-is, you'd be better off just crouching behind the hillside.