Yes I've beat Mile High Club, maybe 2-3 times, it's a biotch. I never thought I could beat them on vet, but you just have to practice and find a strategy. Some missions may be good via camping, some may be good speed running it, you just have to find out.
Homeland Security took a while for me. Basically you want to get the Sentry that you start off with, and run to the diner (it's right next to the Gas Station you start off at). So now you have one Sentry gun from the Gas Station, and one sentry from the diner. Deploy the two behind the counter, and it should last you about 3 waves (also grab the M240 w/ ACOG). By the 3rd wave, your two turrets are probably blown up and useless. If you're overrun and your turrets are gone, STAY prone behind the counter! It offers good protection and you can camp there for a bit.
When you get to the 4th wave (with the BTR), kill everything BUT the BTR! Leave it so you can run to the other side of the map (obviously use common sense and not run while the BTR's right in front of you LOL), go to the top of Nate's, deploy the turret there on the rooftop, and go to the bank, get that turret, and run back to the diner and take it with you. So now you have one turret to help you in the diner, and one turret on a rooftop on the other side of the map, that's going to shoot everything. When you feel you've got everything set up, destroy the BTR and start the last wave...
If you'd rather see it, see here:
http://www.youtube.com/watch?v=CQ6LfpZ4LHA
Attila16 is pretty awesome on vet. Some missions can be done way faster than he's done but he does a good job nonetheless.