What does the idiom a hound on mean?

The idiom "a hound on" is not a common idiom in English. It's possible you've heard it used in a specific context, or it might be a misheard phrase.

If you can provide more context, I might be able to help you understand what it meant. For example, was it used in a sentence like:

* "He was like a hound on the trail of a rabbit, determined to catch him."

* "She's been a hound on my case all week."

If you can give me more details, I can better understand the meaning and potentially identify a related idiom.