3 IRD's in a house big enough but what's the best way to keep clean???

I don't mind weather (apart from strong winds) but lately this weather has not been much help to me at all and having 3 gorgeous Indian Runner Ducks on a clay soil grassed area - well you can imagine just how it looks right now!

Fair enough, mud will soon turn to dust in a few more weeks time when it all changes in true Brit weather style but what about their house??  I made them a house which has ample height and space for them to pad around in and they are closed in with food and water at night (being at a museum I'm afraid they do have to go to bed to keep safe a little earlier than those who live with you on your own land).  The two girls leave me an egg each, every morning without fail bless em and of course in true IR style they BURST out that door as soon as it's opened and leg it round thier bit of land, flapping and ranting to catch up on gossip from the chickens.

Anyway, here's the thing - what's the best way to keep their bedding clean?? And therefore their eggs....

At first I used straw as that was what I had to hand at the time and then I used what I use for deep litter for the chickens, good old wood shavings and this seems to work better and they are now appearing to keep a corner of the house clean for nest egging.

I change this properly once a week and after about half a week depending on what it's like I top it up a bit.

Anyone else know of a better way that would help at all?

Thanks if anyone can help at all xxxxxxx

I don't keep ducks, but have a muddy area the chooks play in. The best answer here was to use wood chippings around the entry to the coop. This stays fairly clean and seems to act as a doormat. Cheap and easy to replace; you might need it contained in a wooden perimeter to keep things tidy. HTH