This is a rather advanced method of protecting against clickjackers, who might be knowledgeable enough to surpass your basic filters. You may make the attack much harder if you include a one-time code in URLs to crucial pages. This is similar to nonces used to prevent CSRF but in unique ...
If you have any friends or colleagues using an older version of Internet Explorer (or any old browser), help them upgrade to the latest version of Chrome, Firefox, Safari, or Opera. You might even want to show them a CSS3-rich or HTML5-rich website in a modern browser and compare it...