commercial low-flight safety

Some duck hunters want to hire me to overfly a network of ponds in Oregon so
that they can scout the hunting range ahead of the season, with the request
that they want to "get down low."

Based on the terrain and the shape of the ponds, it would be easy to set it
up like a basic closed-traffic pattern at 1,500 down to 500' AGL, and I'm
sure pilots in Alaska do that sort of thing in their sleep. (The hunters
are Alaska natives and used to chartering these sorts of flights, and I've
flown with one of them several times noncommercially so they know me and I
know them.)

I told them 500' is as low as I would commit, esp without first observing
for flying birds, tall trees, trigger-happy hunters and other possible
hazards. It's a photo mission and we're launching and returning to the
same field, so it's all legal. The terrain is a very wide, flat,
unpopulated valley floor which is not in a protected wildlife area. The
aircraft is a C-172.

My question is, how low would -you- go for this sort of flight assuming the
birds aren't around and there aren't of Cheneys on the banks looking for
something in the air to shoot at?

Thanks, everybody!

-c
(CP-ASEL-IA)