Wood Duck ... unlike Woodies that are cavity nesters, Mallards are canopy nesters (like to nest under a shrub or large plant they can hide in (avoid predators - especially avian). Geese, on the other hand, prefer to nest in the open (papa stays to help guard the nest). If you want that Mallard to pull off a successful clutch of eggs, cut off 1/3 of a 55-gal. barrel (metal or plastic - cut it - around the barrel -on either rib on the barrel). Get a strong metal pole (the kind - 8' - they use for stop signs or other signage), wade into your marsh - drive the post into the bottom of the marsh - bolt the barrel on the post about 3 feet above the water line at normal pool- now it is essentially a tub (with holes drilled into the bottom for drainage and a door-slot cut out of the side of the barrel - little ducklings have to get out of the barrel right after hatching) about 3 feet above the water line. Next -and this is important - rig up a top / canopy over the tub ( I would use the top of the barrel (the one you used to make the tub) ....I suggest you .... cut off the top as a flat piece with the same diameter as the tub (leave a 6" wide and 10" long tab attached to this round top section) - tab is cut out of the side of the barrel on this top section - then, use a piece of 2X4 or metal (better) post (3 brackets/posts is best - one in back and one on each side) attached to the tab AND the rear of the tub to create a top 18-20 inches above the top of the tub section. In late Feb / early Mar, place wood shavings in the tub and get ready for a nesting duck.