|1.||I got your six|
Basically means "I've got your back." Comes from the old pilot system in which directions correspond to hours on the clock, where 12 o'clock is forward and 6 o'clock is behind. Thus anyone behind you is "at your six."
Watch out, dude. There's a creep comin' up behind you but I got your six.
|2.||I got your six|
another way of saying "I've got you covered" or "I'm backing you up".
letting someone know that you'll be around to help out or protect them in any way you can.
"they don't know that this is a sting op and a major heat score is about to go down so you gotta keep your cool. don't worry G, we got your six."