My ducks free range just like the dogs do. They have access to the same fenced 4 acres the dogs do. But they stick to the 1/2 acre or so that is closest to the house. That is their safety zone. I've marched them out to the far back before, but we get there, they take a quick look around before running back to the house. They know where they are comfortable.
As far as training them. I didn't.
Maybe around 4 weeks or so, I'd start putting them out in the yard while I was out there and just hung out with them. When I was ready to go in, they went back to their area on the deck. Eventually I left them out without staying and just checked on them, a lot. And then I started leaving them out there for the day, they would come up to the deck as it was getting dark. I don't know that I was so much training them as I was just going with my comfort level.