I'm definitely not an expert, but I have a duck with similar issues, so thought I'd share what we have been doing.
Our male Pekin, Quacks (he came with the name lol), has an issue with one of his legs where it's not strong enough to support him so it ends up sticking far out to the side when he stands up, and has caused his leg to be crooked at his ankle. Our vet recommended hobbling him to keep his leg under him and strengthen it. It's working some, but the poor guy has a lot of difficulty getting around and spends most of his time lying around. We haven't had him very long and had never intended to own ducks, so have been forced into the deep end, so to speak, trying to care for him (he was an emergency re-home from a friend).
Once we started hobbling him, we moved him to our back deck where we could keep a closer eye on him. He & his mate had a repurposed dog kennel that we put straw in for bedding, and didn't immediately realize that because he was lying in wet straw all the time (despite frequent changing), that it was damaging his belly feathers. He lost all the water-proofing because he wasn't able to properly groom himself and the feathers started breaking off. As soon as we realized what was happening we got rid of the straw, so his belly no longer stays wet all the time. They now have indoor/outdoor carpet that drains water easily & dries quickly so even if his belly is wet when he lays on it, it tends to wick the water away and help him dry. He is currently molting and thankfully new feathers are growing in. Although he has access to a pool, he has a lot of difficulty once he gets into the water because his balance is off, so he mostly just walks up to the edge and splashes water on himself to bathe. This has actually helped keep his belly dry though, since the feathers don't soak up so much water this way. When he wasn't able to stand on his own I would hold him up at the edge so he could bathe.
We also had to deal with sores on the bottom of his feet, especially the foot on his bad leg because he essentially walks on the inner toe and pushes against it all the time when he's trying to walk or stand. Our vet said we caught it before it actually developed into bumblefoot, but we bought him some neoprene shoes to protect his feet and that has helped to prevent new sores from forming.
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