To have ipguard start at boot time, add the following line
to /etc/rc.conf.local, substituting the flags as needed:

ipguard_flags="<interface>"

and to /etc/rc.local:

if [ "${ipguard_flags}" != "NO" -a -x ${PREFIX}/sbin/ipguard ]; then
	install -d -o _ipguard /var/run/ipguard
	${PREFIX}/sbin/ipguard ${ipguard_flags}
	echo -n ' ipguard'
fi