We use Connectotel to filter access, but students are constantly finding new proxies to bypass the filters to get to Myspace, Bebo, etc. I must add about 10 new proxies a day to the block lists.
We added a deny rule:
This stops 90% or so of the proxy server sites. It won't stop the user from getting into proxies, but they won't get anywhere from there.
In addition, don't forget to add a rule to block Port 443 as most proxy sites offer SSL access.
Disclaimer: As with everything else at Cool Solutions, this content is definitely not supported by Novell (so don't even think of calling Support if you try something and it blows up).
It was contributed by a community member and is published "as is." It seems to have worked for at least one person, and might work for you. But please be sure to test, test, test before you do anything drastic with it.