Welsh Harlequin Ducklings Video

Have you seen a ducklings tail waggle as it walks? It's not really its tail, but the whole rear end swaying side to side as it desperately tries to keep up with its siblings.
They are fascinating little birds, and I can see that they will easily become an obsession for me.
The fact is, they are not exactly little birds, even when they first hatch I was amazed at their size.  Now two weeks on they are a substantial little unit and I think mum, Treacle, is a lot more relaxed with them possible due to their size and agility.

They are still yellow at three weeks as you can see in the photos and video, but the dark colours are starting to creep through at the rear end.

I'm under no illusion I will need to create some room for them longer term and at the rate they are growing this could well be in the next two or three weeks.  I have an area that is currently covered with bushes.  So I will need to dig them out and level the ground.  But I am undecided on what to use for the floor.  I have seen pebbles, stone, and concrete used.  I know I can not leave bare earth.
There is also the decision on the enclosure.  The original intention was for them to live down on my allotment next door to the chickens, but with the break in and theft last month I will not be keeping any more of my pure breed birds on the plot.  So I need to accommodate the ducks in the back garden, certainly for the next 4 months or so whilst I keep looking to rent some land.  
I'm considering buying some poultry netting to create an area for them it's relatively cheap and quite flexible.