Check your six 

A term often used and popularized by the military to check at your 6 o'clock position. Which would be right behind you at any given point.

Sergeant: Private, check your six and tell me if you see any bogeys.

Private: Yes sir!

Check your six by CallmeCj December 30, 2012

check your six 

An expression used to inform someone that there's a target at their 6 o' clock position.

1: "Check your six."
2: "... Damn."
1: "Told ya."

check your six by n00bert December 26, 2008