Here in East Texas ducks don't need a shelter, but for some reason when it got hot out this summer, they all started spending the night inside the horse stall. All five of my horses either stand up tight together in the other stall, or feed from the hay ring all night long. The geese also sleep with the ducks. The guineas are in there too, but they all stand on a railing that I have in case I ever want to put a gate on that stall to keep a horse locked up and away from the others. In your area, a shelter of some kind might be needed.
To get the guineas to stick around, you have to lock them all up in a pen for a few weeks. Then once a week, you let just one out. It will spend all of it's time trying to get back in and be close to the other guineas. It just takes one guinea in a pen to keep all the others around. Once you let them all out, they wonder. They break up into groups that change constantly. I usually have two groups, but sometimes three and four. Size will range from all of them together, to a dozen in one group, four in another and one or two that can't decide and race back and forth between groups. Every night at 6 pm, or just before dark in winter, we feed everyone. Horses, goats, pig, guineas, geese, ducks and chickens. They all show up for feeding time. It's actually kind of crazy fun to see them all eating at the same time, then trying to steal each others piles of food, even though their pile is the same and they haven't finished it yet. Then after the horses have finished their feed, they steal what's left.
To let the ducks and geese go, we clipped both wings. They can fly enough to get away from trouble, but not enough to leave. By the time they grow out their feathers, they have no reason to leave. They will fly around the pond, or if out in the grass, fly back to the pond, but mostly they just walk and swim everywhere.
I have 7 geese and I think about 20 ducks. I do not have a poop problem. I guess they either poop in the water, or out in the grass. They have five acres at night to wonder around in, and another 7 acres during the day. In my opinion, it would take ten times as many ducks to create a problem with smell or too much poop. I also get 4 feet of rain per year on average, and that probably has something to do with cleaning up the poop. Or it could be the horses walking around the barn all the time keeps the poop from building up. Horse hoofs make sure nothing grows where they walk, or builds up.