Has anyone got any advice or examples that I could look at regarding puppy contracts?

I have always built up a good relationship with the new owners of my puppies and they have always promised to come back to me if they had a problem and could no longer keep their dog. However, I've heard some horror stories from other breeders and I'm now considering giving out a contract with each puppy, but I've never seen one and I'm unsure what it should include.

Any advice would be gratefully appreciated.