In the map Kino der Toten, get to the stage after turning on the power.

In the front-center of the stage is a podium. Finish a round except for a crawler (preferably a slow one).

Get juggernogg (or only let him hit you once at a time).

Get on the steps that lead to the podium (they face the back of the stage) and have the crawler follow you up.

Get your back up against the podium and as he hits you, jump and pull back and after a try or two, he will knock you up onto the podium where the zombies can only hit you if you hang off of the spot you came up, otherwise you are untouchable up there.

You can hang off of the side to get them to come up on stage, otherwise they pile up in front of the podium.