This is a tricky challenge. The goal is to keep all enemies out of the red endzone.
It's a good idea to have the miniturret launcher leveld up to at least four. Place out a couple of turrets across the arena, to give you a decent coverage area. Use the hunter mine launcher till you run out of ammo. Next use the arbiter (put the napalm mod on it) to clear out the executioners and zombies. If all of these run our of ammo use the magma cannon to take out the swarmers.
The most effective strategy for Endzone is the Shield Launcher with the Shock Omega mod attached. Create a wall by dropping 3 shields in a straight line about halfway towards the far edge from the zone. Almost everything spawns on the edge opposite your zone. The occasional giant mecha scorpion will drop behind your shield wall, just dispatch them with the heavy weapon of your choice. The swarmers are the real threat to your zone, but every time one of them touches one of your shields, they all get an unhealthy dose of blazing electric death. Just keep an eye out for when the timer runs out on the shields....
The description for this match states that if enough enemies are in the endzone, Ratchet's deadlock collar will explode.