Okay, ducks abandoned as a bad idea.
Happily, am wearing blokie down to coming round to the idea of chooks - on the understanding that I clean up the poo and his garden isn't torn to shreds...
So, have come up with a notion of building an arc (that triangle shaped house with an attached run) that fits onto a wooden base that's filled with bark chips.
the wooden base would fit the entire arc and run. It'd have extra strong chicken wire on the bottom to keep the weight down, and the rats out. the base would be covered in bark chips, so the chooks can scratch and insects from the grass can get into the run for pecking up. But, the chooks can't scratch down into the actual grass.
The run attaches to the house, and all bits come apart to move round the garden.
Thus far, my joinery skills extend to flat pack furniture and putting up shelves. But, there's lots of plans online. And, I can pimp my arc if I build it myself!
Whaddyathink? What is the obvious thing I haven't thought of that explains why everyone doesn't fit a fox-proof, rat-proof, rip-up-the-lawn-proof chicken house?