Border manager and Gateway

At our campus we are running bordermanager 3.7 Proxy and firewall.

The problem we have is we want to force the user(s) to go through the

proxy and not put the proxys ip address in the default gateway setting

under your tcp/ip network settings in windows. We have found that if
they
put our proxys ip address as there default gateway they have
unrestricted
access to internet and downloads and can NOT be monitored.

How do we acheive fixing this?

Thanks in advance

Troy Pieterman
I.T Technician
Woodleigh School