Through the Wall
How To Unlock: Shoot an enemy through a wall.
This is an easy trophy. As soon as you see that an enemy is hiding behind a wooden wall, try to shoot him with you sniper rifle. You have to kill a soldier by firing through the structure. You should get several opportunities to get this by playing normally. But the easiest early place to get this is in the very first level.
After you rappel down into the refinery, soldiers will spawn on the far side of the map. There is also a guard tower over there. Take out all the others first, before going for the guy in the tower. There is a nice spot under some storage tanks on the way there that sets you up nicely for the shot. Make sure to aim at the side wall of the tower, and try to hit the guard as high up as you can. Two or three shots to the body should be enough to do the job. Or if you can manage it, a single headshot will work.