Deny access to radio websites

Hi,
could you please help me to deny access to radio websites using ISA Server 2004. I have tried blocking all the protocols of the streaming media and also the audio but it continued. I have then blocked some radio websites which were listened to and it worked but when one website is not available, the clients will go to other websites until one which works.
So, it is not practical to block one by one. Is there a method to block all the radio websites?

Thanking you in advance for your help