Ghost pro

That is the hardest one...no one seems to use the sentry gun anymore.  I think got mine in demolition.  In one of my levels I had to play with friends and destroy one of theirs.  My friends are jerks and kept killing me...finally got one.      

Ya I got mine from luck. Someone must have used a care package. Just wait for the time, it will arrive.

why can tit just be a turret of any kind. like the sentry and the rocket one that takes down air support.

I'm having the same problem as you, all I have left for Ghost Pro is destroying a sentry gun.  But like you said, nobody seems to use them.

    Its definitely not the easiest challenge but I usually have it done by the time I get everthing else completed or shortly after.

    Use hacker ........ and if you know someone is using a sentry gun, try to stay in the same lobby with them as long as you can.

    Letting the enemy steal your own is a good idea, but I've never had to resort to that. I just make it a priority from the instant I buy the ghost perk.

[quote user="RyuNeonNinja"]

why can't it just be a turret of any kind. like the sentry and the rocket one that takes down air support.

[/quote]

Because the Sentry Gun actually shoots at approaching enemies.  And the SAM turret just shoots enemy aircraft.  The point is you have to sneak up behind the Sentry Gun while using the Ghost perk.  There's practically no skill in killing a SAM turret.

Ghost and Hacker on every class until you get it. Sometimes I got it done before rank 20 sometimes it took until rank 30.

I've never had a problem with getting it by throwing my sentry gun at the enemy and running away.  I usually get it done in one try.

Very tough one to get.  Like the guy said earlier, you need to have both Ghost and Hacker to make it easier.

    I really think a lot of it has to do with being willing to sacrifice a bit.

   While they arent used a lot, considering you only have to destroy one, compared to the quantity on the other two challenges, you are bound to run into one.

    But I think a lot of times its easy to forget in the beginning, or think " well we're winning, and I have plenty of other challenges to do ..... sooo I'll just wait"  Then when you have everything completed but the sentry gun, you may not see one for a while.

     Be prepared ........ they are easy to get, so if someone is equipped, you are sure to see several of them over a few matches.