Wallhack 

If you're sniping from Mc Millan's perspective, you'll notice that the enemies spawn from 2 locations, one near the dried swimming pool (which you've passed through earlier, towards the left-end corner from Cpt. Mc Millan's perspective. For easy description, let's call it "spawn A") and the other one towards the right-end corner from Mc Millan's perspective (let's call that "spawn B"). The latter only spawns troops after the arrival of the enemies' choppers.

After dropping Mc Millan into his "camping site", proceed stright towards spawn B. There, you'll get to see a giant door where troops will start pouring out after the enemies' heli arrives. From that location, you'll also get a clear view of spawn A. Plant all of your claymores to cover your back and have your M21 (or whatever gun you have, it's best you have an AK-47) aiming at spawn A. The moment you see troops flowing out from spawn A, DO NOT WAIT TILL MC MILLAN GIVE YOU THE ORDER TO SHOOT. Unload your ammo at them upon first sight!!!

*Then as scripted, all AIs will go prone for a few moment, then doggies will start rushing out from the pool to munch them.... bla bla bla*

Try to take out as many guys as you can while they're in the chokepoint. Mc Millan will pick off the leftovers (If they still manage to sneak past Mc Millan's marksmanship, that's where your claymores come in handy since they'll most likely come and backstab you.

When enemies' choppers are arriving, you'll have a brief moment to replenish your ammo and change your camping spot to spawn A. That's right, go all the way into spawn A!!! Since you're there, your enemies can't spawn in front of you. This time, keep your gun pointing at spawn B. Hold out until friendly chopper arrives to extract both you and Mc Millan. Be warned, there will be a couple of dogs coming your way whilst you're in spawn A.

Wallhack