One of the ETSN members present sends everything through one box, including the connection to the county. To block a site requires restarting the firewall, which could destroy the connection so the tech has to wait. When a system that performs a variety of functions gets impacted, it will stop doing one activity to do another one. A separate device insures that your filtering is always working. A request was made for a spreadsheet of the systems used by district and Steve said he would put that together.
Control is an issue with filtering.
It is possible to filter to the point that nothing gets through. Administratively the hardest issue is maintaining the system which requires having an infrastructure in place.