Blocking iphiding sites

Hi Everyone,

In my Redhat linux 9 system, I am using Squid as proxy. Using
squidguard I used to block the unwanted sites. But some users are
still accessing the blocked sites using some
Iphiding sites(example: hideme.com).
Apart from blocking the ip hiding sites, is there any other way to
stop the users from accessing the blocked sites.

Is there any ports I can block ,
which is used by the iphiding sites. Any specific ports are used by
them?


Thanks in advance