Having someone’s six, or watching someone’s six, is an old military term that means “I’ve got your back,” or “I’m covering your rear.”
It comes from the hands on a clock, which resemble the points on a compass. In aviation “six” corresponds to the “six o’clock” position (on a compass that would be 180 degrees), which is directly behind the aircraft (and “six- o’clock high” means behind and above the aircraft; the movie “Twelve O’clock High” referred to enemy being directly in front and above the aircraft).
Okay,thanks for the info.