Dead gateway detection

[Gabriel Gunderson]

I'm setting up a box with two connections going out to different ISPs
for a small business in town.  The second was just for a backup but they
wanted to be able add its bandwidth to that of the first for out going
traffic.  On a failure the traffic goes out the one connection.

I think I have it all working but I'm still looking for an elegant way
to detect a dead gateway.  I have a cron job that uses ping to check
each gw.  It works but it's a little clunky and only checks every
minute.

What have you all done to detect dead gateways?

Thanks,
Gabe