[CentOS] Define HTTP proxy system-wide (Squid and Squidguard) ?

[John Doe]

From: Niki Kovacs <contact at kikinovak.net>
> I'm currently configuring Squid and Squidguard for filtering web 
> access in a public computer room. So far, everything works fine.
> I know how to configure Firefox to use a proxy, but there's no way to 
> protect that configuration, e. g. a more knowledgeable user might 
> circumvent this configuration. Is there some way to configure an HTTP 
> proxy system-wide?

I think you might have to go this way:
http://wiki.squid-cache.org/ConfigExamples/Intercept/IptablesPolicyRoute

JD