What is 4 player trick?

While still being quite far from my 100m per wave per person goal, a new ways of gaining score fast had been discovered, basically the way that it worked is you had 4 people in your party, then kicked them after zombies stop spawning.. then your left with 4 people worth of zombies and one player to collect all the score. Knowing this, I set out to make a new side score base.. but this time be able to handle 4 players worth of zombies. After I recreated my previous base, I knew there was no way in hell it was going to survive with 4 players worth of zombies. The worst parts of the base were the 2 sides, and the center. With the fast shooting towers long gone, I had to put mages in the front of the base, and slope in the sides of the base, which also dramatically helped to increase the attraction to the entrance, now with about 65-70% of the zombies going to the ent.