Early on in Dead Ops, the Mamaback will destroy the teleporter, forcing you into a portal that takes you to the Wild. In this area there will be giant zombie heads that infinitely spawn zombies. Take full advantage of the powerups that spawn to quickly take out the spawners. There are also spike traps that insta-kill you if you touch them, so watch out for the sparkles on the ground that indicate when the spikes are about to pop up.
There's going to be a ton of zombies, but just push through to the end of the area and step on the teleporter pad to exit the Wild and unlock the achievement.