session problem

Question

session problem when i click logout it redirect to logout.aspx

 

 

but when i click backward button it remain goes to to logout page

 

 

how to solve this

 

 

 this is my code for logut

 

 protected void Page_Load(object sender, EventArgs e)

    {

        Session.Abandon();

        Session.Clear();

        HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.NoCache);

        Response.Cache.SetAllowResponseInBrowserHistory(false);

        FormsAuthentication.SignOut();

        Response.AddHeader("Refresh", Convert.ToString((Session.Timeout * 5) - 120));

        Response.Redirect("login.aspx");

    }