How To Block Skype using Squid3?

I have just installed Squid3 on my server and trying to block the Skype messenger. Still no luck. I tried to add the rules in Squid wiki (http://wiki.squid-cache.org/ConfigExamples/Chat/Skype) to the end of the squid.conf :

# Skype

 acl numeric_IPs dstdom_regex ^(([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+)|(\[([0-9af]+)?:([0-9af:]+)?:([0-9af]+)?\])):443
 acl Skype_UA browser ^skype

 http_access deny numeric_IPS
 http_access deny Skype_UA

 acl validUserAgent browser \S+
 http_access deny !validUserAgent

But none works. How to block Skype? Please help