Door lock codes and other sensitive information should be managed carefully should you decide to add it to your guide. First, ensure that any topic you add a sensitive code to is locked (privacy protected). While locked content is blocked from the general public, it should not be considered as secure as a typical username/password as guides are instead protected by a security hash.
Therefore, and secondly, should you decide to add a sensitive security code we do recommend making it a habit to change that code on a regular basis (perhaps every month).
You could also consider sending sensitive information as part of the individual invite message that goes out with the invite link.