Checking Routes/Gateways For Good Connection

[Don Tek]

 I've recently implemented a firewall with two internet connections 
using multipath routing and round-robin outbound load balancing.

I am looking for a solution from the shell to detect failure of these 
two internet gateways so I can force routing and pf changes from a script.

I need something more robust than simply checking to see if the 
interface is up or down.

I have managed a solution using traceroute that allows me to accomplish 
half of my goal.  I can detect a failure and "down" that route, however, 
once I delete the default route from the routing table for the failed 
connection, I can no longer test it with traceroute.  This is because it 
doesn't appear to me that OpenBSD's traceroute allows forcing an 
interface to work on.

I am looking for better solutions from some of you more experienced 
users.  Any suggestions are welcome.

don..