The following page on the Squid website demonstrates rotation of IPs for varying times of the day:
http://wiki.squid-cache.org/ConfigEx...on_time_of_day
All you need to do to rotate this for all requests and not keep it consistent is remove the access control list and add:
balance_on_multiple_ip on
and change them all to the same group removing the Access Control List.
Something like:
tcp_outgoing_address 192.0.2.1 ip1
tcp_outgoing_address 192.0.2.2 ip2
tcp_outgoing_address 192.0.2.3 ip3
balance_on_multiple_ip on