I have a bizarre little network here consisting of two home-based
dhclient-setup internet links.

I also have a web-server sitting in here. If traffic comes in through
router #1 (and hits the web-server's 10.x address) I very much want
the answer to go back out the 10.x interface. If traffic comes in the
other link (directly connected) I want the answer to do the same.

How do I do this? Is there some sort of routing flag? --To simplify,
why would traffic sent to 10.0.x.x be answered on a 64.x.x.x
interface? Should I be reading something to understand what's going on
and how to fix it?

Currently I have a rdr and a map on the router (a NetBSD machine) but
this means I can't collect any stats for traffic coming in through
that IP address. Doh!

Thank you,
Marc