GOT YOUR BACK
1) An expression assuring someone that you are watching out for them.  Comes from making sure you are safe by watching what's behind you when you're busy looking ahead.

2) Can be converted to a threat: "Watch your back," from the possibility someone might injure or kill them from behind when they aren't lookin.
Iono about dis...

Don't trip, Son.  I GOT YOUR BACK.