How to require a "Re:" for subject-based threads?

Is there a way to require a "Re:" to procede a subject before that is 
considered 
to be part of a thread?  I am having problems with new messages having the same 
subject as very old threads and thus showing up at the bottom of my thread 
index, and as belonging to a thread that they really don't belong in...

If this is a FAQ, I applogize...  I did check the docs, but couldn't find 
anything.

Thanks,
Jamey