i noticed on a few maps that you can spawn trap the enemies. if you are camping out somewhere they almost always spawn in the same places. if ur playing co-op especially on the tier 1 maps where you have a helo just about every round after 22-23 except for jugg rounds. if you use a predator at the beginning of the round you can reccie the spawn points from the air then when the helo is up have your partner disstract it whilst you go lay your traps. obviously you have to increase the explosive capacity as the waves go on but this is a simple matter of dropping progressively more c4 in front of your claymore.