In my opinion logging off for each page isn't suiting the purpose of using sessions. Everone use sessions to get the track of users browsing the different pages in the same site.
And deleting the track for each page seems useless.
Instead of doing this that way, you better specify a time limit for deletion.that's a simple check in the logoff.php whether there is a traffic between client and server in the bounds of time limit. If not delete the session data. Otherwise wait for the next logoff request.
