You could make a new folder in /var/squidGuard/blacklists and add a couple of files that are similar to ones you already see there.
# For example: Chat ( messenger )
domains expressions urls
Your domain list file may start like this...
Your expressions list may look like this...
And url list file may look something like this...
Don't forget to initialize the blacklists ( takes a loooong time )
squidGuard -C all
You might also consider adding an acl regexp
Webmin is your friend!