[The Milk Man 09]

I got the six star achievement by flying a helicopter over one of the locked islands and then Flying around apparently if you are high enough they wont even shoot at you. Kinda a wimpy way to do it but I wasn't even thinking about getting the achievement until it popped up because it was the first time I was in a helicopter and I was trying to do stunts with it and I was way up high because I didnt want to crash.