I have a firewall with three working NICs. One hooks into a cable
modem. One into ADSL. The third into my local network.

Problem: Cable and ADSL both try to convince my dhclient that they are
the default route.

Details: Cable has more bandwidth, but ADSL is a good backup. I don't
want to be forced to use two more machines just to do outgoing and
incoming (via DNS round-robin at first) load balancing.

Has anyone else done this without completely re-writing the
dhclient-script and doing clever sneaky custom code-type things?

Any hints? Pointers to other projects? Rotten vegetables for bringing
up a regularly hashed topic?

I would be a perfect guinea pig to help you test ideas--not only do I
have the ability to actually read and understand code (even C!), but
I'm a nice guy with practically limitless patience to boot! :)

Thank you for any help. When we're done I'll be the one to write the
FAQ and save you the trouble.

Marc