Getting the Sacrificial Lamb achievment (Black Ops)?

Ok, so I'm a total newb achievment horder (at least I admit it!) And I've been having trouble with this achievment, so I cleared my update cache so I can do the splitscreen five glitch on the table. So I do everything and get whole bunch of points, then I leave a zombie crawler alive and jump both of us off the table, now the problem is the crawler dies in like 5 seconds before I can even get to the elevator. What's the deal? Have I done anything wrong in my strategy? Also any people who feel like flaming me for glitching are welcome here as well, I think its quite funny. Also, when yahoo gave me what category it thought it was it said food and drink...