Cisco Routers :: RVS-4000 Internet Access Policy Does Not Block Listed Domains

We have an RVS-4000 router that we use as an Internet gateway on our school network.  I am trying to set up an Internet Access Policy to block some specific websites by URL using a domain name.  I set up the policy, and added a PC to the list using the mac address, and the blocking did not work. I went back to the list and added the IP address of the same PC, the policy still did not work to block the domain.  I rebooted the router, cleared the Internet Temporary files and history on the PC, and the policy still does not work.  It acts like it is going to block access to the website because it takes a long time, but it will eventually connect.