For those of you having a hard time, how about the ability to gain this achievement WITHOUT ZOMBIES?
Well now you can, look at the video and you'll find out how =)
Downside you'll need a friend.
Do this on Dead Center survival mode, but don't set off the zombies yet!
For those who can't see the video basically you need to get your friend to climb up the stairs to the highest point on the map then jump all the way down. This will kill him and you can shock him back to life. Reload the dead center survival mode, rinse and repeat and you're done.