hound or an animal down
To hunt, chase, or pursue someone relentlessly, until they can be captured or apprehended. A noun or pronoun can be used between "hound" and "down." Police were able to hound down the suspect en route to Mexico.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
hound someone or an animal down
to pursue and capture someone or an animal. I will hound the killer down if it takes me the rest of my life. I will hound down that killer if it takes years.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.