A little bit of good news. I put the two ducks in a dog cage in the garage last night. This morning I heard light quacking from a clump of weeds. One of the Indian Runner ducks, who had been escaping from the chicken pen, turns out went broody and has a nest there with 6 eggs.
So as it stands now-- 3 living ducks (one of which is the Rouen mallard), 1 duck confirmed dead (Rouen female), and 1 duck I guess should be listed as missing-in-action, presumed-dead.
I need to talk to the hunter neighbors about how it would be if I got a hunting license. Their territory here, as I understand, has its maximum number of members-- people wait for the old ones to retire to get in-- but maybe they could make a special "only killing foxes" category of membership for me.