logout problem

Question

I am tacking user logged and logged out  time in data base but i have one problem
That is: If the user close the browser instead of clicking on Logout button, How can I catch that event. Because if the user login, I will tick the status field of that user in my Database, so that if they close the browser instead of clicking on Logout button, I cant uncheck the status field of that user & logged out time in my Database.
Can you show me how to solve that problem?
 
plz give me the detail solution or some code fragment..

please suggest.


Thank you in-advanced!