Wildlife ponds and ducks

I currently live in London but hopefully later this year I will move out to the countryside. I have been contemplating the possibility of keeping some ducks but as I understand it they can destroy a small pond through overfertilisation (droppings) and by eating everything.

I am keen to have another wildlife pond and will hopefully be creating another meadow ( old one here: http://www.deepblue.uk.net/uknature/pages/meadow.html )given adequate space.

I particularly like the Aylesbury duck and would like to know what is the smallest size pond that would accomommodate 3 or 4 such ducks and still sustain wild insect, plant and fish-life?

Thanks for your help,

Matt

PS - I found this site that I rather like -Jane's Cottage Ducks - http://www.ducks.fslife.co.uk/