on somebody's tail

on (one's) tail

Following or pursuing very close behind someone. The cops are on our tail—we have to lose them in the woods. Why is this guy sitting on my tail when I'm already going over the speed limit?
See also: on, tail

on somebody’s ˈtail

(informal) (of the police, a spy, etc.) following behind somebody very closely: I had the feeling there was someone on my tail.
See also: on, tail