FormsAuthentication.SignOut is NOT working

Hi..

I am trying to create logout link. When I click on the logout, it is taking me to the logon.aspx page. that is good. But, when i press the back button, it is taking me back to the default.aspx page - it should not.

This is what I have for logout:
        public void LoginLink_OnClick(object sender, EventArgs args)
        {
            Session.Abandon();
            Session.Contents.RemoveAll();
            FormsAuthentication.SignOut();
            FormsAuthentication.RedirectToLoginPage();
        }
and in the default.aspx page - form_load:
            if (HttpContext.Current.User.Identity.IsAuthenticated == false)
            {
                FormsAuthentication.RedirectToLoginPage();
            }

I also have some code in the void Application_AuthenticateRequest(Object sender, EventArgs e)
            String cookieName = FormsAuthentication.FormsCookieName;
            HttpCookie authCookie = Context.Request.Cookies[cookieName];
            if (null == authCookie)
            {//There is no authentication cookie.
                return;
            }