logging off the user when moving from the application

[Mack Ait Aoudia]

Hello everybody, I'm looking for a way to make a user logged off when he moved from the application. Actually, if the user signed out or if he closed the window's application (whatever the browser used)he is logged off. But the issue now is: if the user would navigate from my application to another site by writing a new url in the adress bar, his session still active. With the back button he could get the page visited and still logged on. At first, I disabled the cache of pages and the back button display an IE empty page. And if we refresh this IE page, we get the previous page and the user still logged. I'll appreciate any suggestions.