Has anyone tried Aubiose (shredded hemp) for duck pens? It's soft, warm, fantastically absorbent and doesn't develop fungal problems when damp. I use it for my hens and as it's really horse bedding it's intended for a deep litter system where you add extra on top, having removed the worse of the poo, which is easy to do on a daily basis as it coats the droppings and make it possible to pick them up. It's a good choice if you have a riding stables nearby that will sell you a few bales without costing the earth for transport, as Flytes of Fancy etc do. Last week i bought 5 X 22-kg bales for £54 plus £1.80 delivery for the lot, which will last me a year. Contents of the muck bucket are an amazing addition to compost as well.
In the chicken run I also have a permeable membrane underneath the Aubiose, which stops them scratching earth into the bedding and keeps it cleaner. They have a big dustbath for that. Oh, and a roof over the run as well, with a gutter to prevent rain coming in from the sides and willow screening round some of the sides for shade and wind protection. I know ducks need access to water to dabble in, and so they are intrinsically messier than hens, but if you can reduce the amount of rainwater falling on the pen it must be a help. I know that they prefer grass, whether mesh covered or not, but when this isn't available, anything is better than mud, i would imagine.
Here's a link to Aubiose stockist, if interested. I don't know what you think about Aubiose for ducks, dorsetduckowner?
http://www.aubiose.co.uk/stockists.php