how do i call session.abandon how do i call session.abandon if user navigates to otherpage

Hi,
 
I'm new to programming and web designing. I'm trying to build a admin page to website which is already built. everything went on fine. Whenever I log in into the admin page giving the usr id and pwd....it is directed to a form called events. But after going into the event page if I click back arrow in the browser and then click a forward arrow I'm able to go into the events page. I need to stop that. can anybody help out on this....whenever we r logged in and click a back arrow followed by a front arrow I need the session to be logged out......Please help me on this...Appreciate your help....
 
Thanks,
Pavan.