Achievements...
	Rock Warrior...

Complete the following achievements to unlock Xbox Live Gamerscore points.

Achievement	How to unlock
Act I ( 10 points )	Complete Act I.
Act II ( 20 points )	Complete Act II.
Act III ( 30 points )	Complete Act III.
Act IV ( 40 points )	Complete Act IV.
Captain ( 30 points )	Finish the game on Normal difficulty.
Close Range ( 40 points )	Kill 250 people using pistol.(Multiplayer)
Electrician ( 20 points )	Shoot 5 cable lines using sniper rifles.
Fallen Eagle ( 20 points )	Kill 10 birds.
Flying Knives ( 30 points )	Kill 10 enemies with throwing knives.
General ( 60 points )	Finish the game on Hard difficulty.
Heavy Fire ( 30 points )	Kill a total of 30 enemies with Browning gun.
Hold Your Breath ( 50 points )	Kill 250 people using sniper rifle.(Multiplayer)
Laurel Wreath ( 100 points )	Win 50 rounds playing online.(Multiplayer)
One package, Two receivers ( 40 points )	Kill 2 enemies with one grenade.
One shot, Two Kills ( 50 points )	Kill 2 enemies with one shot.
Rookie ( 10 points )	Finish the game on Easy difficulty.
Seeker ( 50 points )	Collect all secrets.
Sharpshooter ( 60 points )	Kill 500 people using sniper rifle.(Multiplayer)
Sniper Expert ( 30 points )	Deliver 50 headshots.
Sniper Master ( 60 points )	Deliver 100 headshots.
Supplier of the Death ( 90 points )	Kill 2000 people.(Multiplayer)
The Protector of Pontoon ( 60 points )	Kill all enemies attacking your pontoon from the riverside on "Weaken The Regime" level.
Through the Wall ( 30 points )	Shoot an enemy through a wall.
You Have to Focus ( 40 points )	Kill 15 enemies using concentration mode.

If you approach certain rocks when in crouch mode you can actually enter them and not be seen. Here you can shoot enemies without being killed. So try certain rocks.