Do any version control systems allow you to specify line level security restrictions rather than file level? I know it would be horrible to maintain. If I wanted to never allow certain strings into the database should I be looking into the notion of hooks and manage all the very sensitive information in that hook layer? How do hooks get replicated from system to system?
Update: Maybe the best way to manage this is to pgp encrypt the sensitive data and those who cannot decrypt it will be left in the dark. Any thoughts on that? Probably not a best practice from a security standpoint.