I have something along the lines of the triplex run. There is Little Fort Knox, a secure house and porch for nighttime and rough weather, attached to a day run with water pans (on pea gravel), a compost-mulch pile they can noodle around in looking for worms, and a door that leads toward some garden areas that they visit with supervision from time to time.
I am still refining things, so in the works are some planting of comfrey and more Good King Henry and other perennials that can grow through the fence so that the ducks can nibble on the ends of the branches but not bother the main stem or roots. In the morning I gather tall stems of jewelweed, and hang them upside down over the fence. The ducks love browsing at head level, and will jump up to nab more leaves. I also provide what I call ladies thumb or ladies purse, a native smartweed. They like to nibble the seeds, and often grab a stem and swish it around in their water bowl.
You can make vegetation available for the ducks, you just need to be creative about protecting the main stem and roots with fencing, or by rotating areas they can play in and replanting with fast growing plants. Buckwheat is a fast grower, and mine really like it when it is young and tender.