How to awoid admin collision in CMS?

[eluser]WanWizard[/eluser]
This is the way ExiteCMS does it.

It also stores an expiry timestamp, which is equal to the session expire timestamp. As long as the session is valid, we consider the user logged in.
Queries on the 'online' table exlude expired results, expired records are periodically deleted in the same way the session library does it.

This approach has a risk. As the timeout is configurable, an administrator could set the timeout to 1 month, login, kill the browser, and go on an extended vacation. And all the time all other administrators are locked out.

I think you have to ask yourself what it is that you are trying to protect other admins against, i.e. why can't you allow simultanous logins? A web application should support multi-user access, collisions should be dealt with in every screen...