Hidden Ops was done in regular mode. Just head in n start spraying (MP5k secondary weapon) and you can get 2 kills with your sniper rifle as well. Also, remember where the hidden snipers locations are as you can easily take them down fast.

To beat your record, you need another partner + set difficulty to regular. Then start and have fun rushing thru the ops. This is how u can beat your record.

For homeland security, head to the building on your left. Hide in the alley and place the sentry gun near the rubbish bin for the 1st wave. Let the sentry do the work.

2nd wave onwards, head in to the diner and camp behind the bar. Place the sentry behind the bar as well. Do not use the 2nd sentry in ther diner until the first sentry dies. Then only pick up the 2nd sentry and place behind the bar as well.

For heli's, u can use one of the LMG gun to take it down.