You can also do it by registering filters. If you're just using a few modules, you could register filters that allow URLs of the proper form (everything in /bboard, for instance) and reject those not on the list, redirecting them to a "sorry charlie" page. Much easier than changing all the pages, but more overhead per page.
Since everything in /admin is normally restricted to administrators, you can leave that open so you can add modules using the UI later (remembering to then add them to the list of "allowed URLs" in your filter).
