Regarding the cookies...

Hi all
  If i click logout from my project it show u r logged out and if i
click back button on browser it goes to the project even i deleted the
cookies.

  i liked the functionality of gmail where i logout and click the back
button in the browser it shows the login page
so i need the same functionality so can any body help me to achieve
this...

                                                     regards.
                                                     Vamsi....