Keeping ducks inside your garden

I’m thinking about getting 3 ducks to keep in my garden. We have 16 50ft permenant garden beds as well as some blackberries and raspberries. I will attach a picture of my plan. I have friends who love their ducks in their gardens.

My questions are:
- what vegetables will they eat?
- what type of fence do I need to keep them out of our yard? The garden is fenced in with welded wire farm fence and it is about 3 yards from our house.
- if I made them a run to stay in when tomato season is happening and I don’t want them to eat our tomtoes, how big should their run be?

We have kept chickens for years, so I know a bit about keeping birds.

Thanks!

I used to have muscovys and an unfenced garden, they didn't do much harm in general they didn't go into it at all, preferring to graze on the lawn and paths. They did like to nibble lettuce and they managed to defoliate a massive rhubarb. They could quite happily fly over the 5ft chicken wire fence round the chicken pen and a couple liked to sit on top of the fence posts (could be cured with wing clipping of course)

After saying they did no harm.. I would never allow ducks into the garden again if I had salad crops in the ground, you know the amount of mess that comes out of a chicken? Well quadruple that for a duck, and it splashes. I would say that ducks need a lot more space than chickens, purely because of the mess they make, any small pen will turn into a slimy stinky mess in just a few days.

What works for me is to let them into the garden for about an hour in the morning. They (Indian Runners) run around and eat slugs, potato bugs, mushrooms and some leaves they can reach. If left any longer they may eat too many leaves or take a nap on plants.
Welded wire works for runners in my experience. If you could keep them around fruit trees for the rest of the day that’s beneficial. Predation is a big issue with ducks. But they are super useful.

In my garden they love the flowers from peppers, cowpeas, and any cucurbits. They are particularly fond of the leaves from peppers and collards, but also eat a bit of cowpea, raspberry, tomatillo, basil, blueberry, and passionfruit leaves. I try to keep them away from all my peppers, cucurbits while they're flowering, and anything young or tender. Otherwise I mostly let them roam around the garden. Tomatoes and cucumbers are special treats and great for training.

We have muscovies and this year I learned some valuable lessons about them in the garden.

1) They will eat young sprouts of things green - meaning snap peas, mustard, beans, etc. They pluck them right out of the ground. They especially loved my corn starts and I had to replant them 3 times before I just put a fence around them.
2) They stayed away from tomatoes, all squash, vining beans, nasturtiums and marigolds and didn't bother with my asparagus or rhubarb plants. I don't know why!
3) They went berserker for the kale.
4) We have 7 foot tall fences around the garden which didn't bother the females at all - they soared right over the top like it was nothing. The boy is too heavy and doesn't fly really at all. So he was just left looking forlorn.
5) The poop DOES splash and so all salad greens or things you would eat raw shouldn't be around them. Not only for the parasitic, potential illness, yuck factor. But because, as I said above, they eat the green tasties.
6) I did notice a decrease in the sow bug and earwig population, but a major increase in the aphid population, especially around the kale and brassicas. I have no idea if those 2 things are related. I'm inclined to think they are.

So overall? The hassle far outweighed the benefit. I will be clipping wings now and relegating them to their own section with their pond and not getting any more muscovies. I like them, and will dote on the babies we have, but won't be adding in the long run. In years past, I allowed my love for them to overshadow the real hardship of putting them in my garden. So I think the best place for them, at least on our farm, is AROUND the gardens and in the orchard - where they can eat all the crunchy bugs and slugs they want while leaving my low to the ground food crops alone.

I started a couple (four) hen rouen ducks this year- as other folks have said, they seem to target kale/cabbage, cowpeas, peppers.  Mine liked garden peas, too.  I took a similar approach to Kris- let them out for a semi-supervised roam of an hour or two while I'm in the garden working, reading, or relaxing.  

Mine haven't wandered, although they have access to a small (2 food diameter) pool and shade, so they may not want to do too much exploring.  I've been able to keep them contained in a fenced area 18" or 24" provided the fence is reinforced, or stiff enough they can't bend the wire down.  They have a tendency to bulldoze through things, more than they fly or jump.