What is the best way to store a unique URL Slug?

I kinda like the way stackoverflow does it. Which is to put both the ID and the slug into the url. Now the slug no longer has to be unique. I believe hulu.com does it this way as well. I think it's a practical solution to the problem.

Most sites don't change the slug for the reason that if a user edits her title it shouldn't break any links to the post that have already been made.