advices

personal conditions of breeding

the fence : 50 cm are sufficient to forbid them some places... but if they panicked, they succeed in passing. If your garden is surrounded of a metal gratin to normal stitches (5 cm), you must put another in the basis, with small stitches to avoid the flight of ducklings.
sow a mixture of herb and clover on the course (the clover will bring the necessary nitrogen to the herb)
think to trees and bushes that procure shade and natural shelters.
if you don't have predators, useless to shelter them in the evening : the Indian Runner duck is as active the day as the night, and it knows very well how to shelter itselves under a bush if necessary ! In spite of all, if your duck is not a good mother, shut up kids the nigth : on the one hand, they would risk to catch cold and on the other hand, they are easy preys.
let them the access of your vegetable garden during the winter, they will limit populations of slugs and others undesirables... If you want to be able to preserve winter cultures (cabbages, spinach, salads...), regroup and surround them, until the tilling of spring, with a rigid metal grating (easy and fast to install or withdraw )...

if your basin has some steep partitions, hang it with metal grating (stitches of one centimeter) to avoid drownings. Stay up to maintain water in good sanitary conditions.
tile the periphery of the basin on around 70 cm of large : you will avoid the mire and will clean with a simple water jet.

to avoid the wheat pillage (especially by sparrows), install an automatic wheat distributor with a pedal. distributor of this type are in the trade but they are badly adapted to beasts with long neck : take a model for big poultries and add an against-pedal and an against-weight. The summer, for ducklings, install a second automatic distributor for small poultries (for this one, not against-pedal).
don't forget to put to their disposition chalky gravel.

Jérôme CHAÏB - Votre basse-cour famimiale et écologique - éditions Terre Vivante 1995
André POCHON - La prairie à base de trèfle blanc - CEDAPA (Centre d'Etude pour une Agriculture Plus Autonome 2 avenue Chalutier sans pitié Plerin) - http://perso.wanadoo.fr/cedapa/