Dynamic IP and pf?

[Christopher McGee]

I have a cable modem that provides a dynamic IP address to the outside 
interface of my firewall(5.3 with PF doing NAT).  If my IP address 
changes I have to run a script to update my dynamic dns and reload my 
firewall rules based on the new IP address. Is there a recommended way 
of doing this other than having cron check to see if the IP addresss has 
changed?

Thanks,
Chris