We have a vague (40 year old) perimeter fence around the property to keep out the predators - in a lot of places it is long gone. We had a problem with dogs this past fall, so I bought a couple of aggressive geese that alert us to anything that comes by. They also keep out the skunks, which have been a problem for us in the past as well.
The only problem I have found with free range is that new birds can and will wander off. I chased a pair of geese around a neighbor's pond for a month, and my Muscovy hens led my husband and I on a wild romp all over the neighborhood when I first released them. Most of my birds stick close to home, but every once in a while we get a runner. I think they are a lot happier when they can come and go as they please though, so if I have to chase one or two every once in a while I'm OK with it.
We don't have a fence right now (its beyond our budget at the moment) Mine like to wander around the neighbors but always come and go throughout the day as the pond is in my yard. I also keep some snack, bird mix or cracked corn in their pen that they come in to peck on throughout the day. My neighbors have a bird feeder and my Ducks go to scavenge over there, I'm grateful to God my neighbors don't mind, they don't go close to their houses though.