ASP.NET

Response.Cache.SetNoStore();

// Code disables caching by browser. Hence the back browser button
// grayed out and could not causes the Page_Load event to fire 
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Cache.SetExpires(DateTime.UtcNow.AddHours(-1));
Response.Cache.SetNoStore();

<META Http-Equiv="Cache-Control" Content="no-cache">
<META Http-Equiv="Pragma" Content="no-cache">
<META Http-Equiv="Expires" Content="0">

//clears browser history and redirects url
<SCRIPT LANGUAGE=javascript> {  var Backlen=history.length;   history.go(-Backlen);   window.location.href=page url }</SCRIPT>

Page.ClientScript.RegisterStartupScript(this.GetType(),"cle","windows.history.clear",true);

protected void LogOut()   
{       
     Session.Abandon();       
     string nextpage = "Logoutt.aspx";       
     Response.Write("<script language=javascript>");             
     Response.Write("{");       
     Response.Write(" var Backlen=history.length;");       
     Response.Write(" history.go(-Backlen);");       
     Response.Write(" window.location.href='" + nextpage + "'; ");
     Response.Write("}");       
     Response.Write("</script>");   
}

bool bTestComplete = (bool)Session[TEST_FINISHED];

//If this is true, the user probably hit the back button, get him back to the thank you page.
if (bTestComplete == true)
{
Response.Redirect(thankyou.aspx);
}

protected void Page_Load(object sender, System.EventArgs e)
{
 Session[COMPLETE] = false;

 //The rest of the page loading code down here

}

protected void Page_Load(object sender, System.EventArgs e)
{

   if (Session[COMPLETE] == null)
   {
        //Then we are in a state that we shouldn't be in, push back to the notification page.
        Response.Redirect("notification.aspx");
   }

   if (Session[COMPLETE] == true)
   {
        //Then the user has already taken the test, push forward to "thank_you"
        Response.Redirect("answerSheet.aspx");
   }

  ///The rest of the page code down here

}

protected void Page_Load(object sender, System.EventArgs e)
 {

   Session[COMPLETE] == true;

   //The rest of the page loading code down here

 }