Special thanks goes to Roughdawg4's roadmap on PS3imports.org
Best way to get this achievement is in Maneater Mode playing on Breakthrough. The reason this level is ideal is because you can shoot the ice flows and jump in the freezing water which rapidly reduces your health. By doing this you can quickly monitor your health. I suggest getting your health down to the final sliver between round 1 and 2. As soon as your health is at its last bar, get out of water and have shotgun ready for Round 2. Wait for the first wolf to attack and shoot as he leaps. If he hits you and kills you while you still killed him, the achievement will still unlock.