I usually just add a small form to the back end database. I set this form as
the start-up form.
The msgbox looks "just" like a system message box, and I simply give the
user the following message:
You don't have permissions to open this datafile
The user then clicks ok...and I do a application.quite and the application
closes.
Unless the users know about the shift-key bypass, then the above is usually
more then enough to keep users out. And...for good measure...you can turn
off the shift key also.
of course, my users all get a shortcut to the "front" end database, and
never really know, or have learned about the backend part anyway (likely,
you started out with users having to know, or see or learn about the
existence of the backend...and that should have never happened in the first
place. However, the above simple form "boot" users out trick works very well
indeed.