The classic "poor man's copyright" is as soon as possible after you've finished production, mail yourself the recording on a CD, the lyrics and maybe even a short little "all rights reserved" kind of statement, and then don't open it. If a dispute ever arises, the court will sometimes
honor this method. It actually usually doesn't hold up, but it is an option and it's better than nothing. Even if you don't go to court, it could be used for private dispute resolution between you and a collaborator.