How to restrict user, if it come at login page by click browser back or forward key (automatic log out and ) then he/she is unable to go further without successful login

Question

Hi
Noe-a-days I am developing a we application using ASP.NET 3.5 with c#.
I want to know that if user once come at login.aspx page by click the browser back or forward button, the user can not go further with out successful log in.
i.e. google login page if we come at its loin page by click the browser button the password text box is blank and we are unable to back the page.
Same thing I want to use in my project.
I user Session to check but it can not help, it is just protect if any one copy the url (of after successful login) and past then come at login.aspx page