On somebody’s tail
Definition 1 of 2
Pro Tip 1/3Physical Pursuit
Used when describing someone physically close behind, like in a chase. 
I sprinted down the street with my brother on my tail.
Pro Tip 2/3Not Literal
It doesn't always mean a literal pursuit; it can describe a metaphorical chase. 
After the interview, I had several companies on my tail.
Pro Tip 3/3Action Scenes
Commonly used in action movies or books to describe thrilling chases. 
The hero raced through the crowd with the villain on his tail.