Research and install transproxy to make sure your users use squid/proxy. I am using sarg to provide nice looking html reports of the squid log. Using this forum and how-tos, I set up squid, squidguard, transproxy, and sarg. Now the users on the network are denied access to squidguard blacklist sites, and all access is reported by user IP, url, and has date and time. With a little configuration, sarg will provide daily, weekly, and montly reports.