One needs to clear the cache such that browser has no history (this will make back/forward button in browser grayed out disabled.) Here are various ways of how one can do it:
One can clear browser history through JavaScript:
<SCRIPT LANGUAGE="javascript">
{
var Backlen=history.length;
history.go(-Backlen);
window.location.href=page url
}
</SCRIPT>
one can set this in logout event:
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>");
}