Hi,
I would use /etc/init.d/squid stop
and to keep squid from starting next reboot, I would
1) check runlevel by using "runlevel" command (output is something
like N6 or N7)
2) move /etc/rc.d/rc.d/S90squid to
the new name /etc/rc.d/rc.d/s90squid
The "s" instead of "S" keeps linux from starting the service...
Regards, René