|1.||Got your six|
I'm following you or I'm behind you; more broadly, I'll back you up/take your side. Also, "I'm on your six". Refers to the six o'clock position relative to the listener (behind).
Car Phone 1: Where are you? I don't see your car.
Car Phone 2: Look in your rearview mirror; I'm on your six.
Joe: Dude, I need some heavy backup for tomorrow's meeting!
Jack: Don't worry man; I got your six.