It may help to understand that the majority of the so called "free ranged" birds are not free ranged in the true sense of the word. They are yarded. That is to say, confined within an enclosure. It may be as small as a run attached to a coop, or as big as one's back yard, or it may be several acres, but they are enclosed and protected within an enclosed area. Key word is "protected".
True free range birds....no barriers at all...... existing within an area with normal predator population.......are birds that are at constant risk of death. It is a battle of attrition. A constant put and take.......you are going to lose birds. Predators will take advantage of the situation and move it for the easy meals. Unless you add to the supply at the same rate as birds are lost, eventually you will be wiped out.
I am aware of one fairly large layer operation near here, they may have 1,000 birds or more......that are truly free ranged. Open the door and let em go. But they are on a general farmstead of several acres that is isolated some distance from any woods by open crop fields and the birds just run everywhere. They may still lose some birds during the day when they are out and about, but not enough to notice or matter. In my mind, they are the exception. My guess is they also shoot any suspected predators on sight. That would include stray dogs. Shot on sight. Word gets out in the neighborhood......you wanna keep a dog, keep him at home.
So what you are left with if you want to keep birds is to establish some type of protective barrier to keep the birds and predators apart. It can be as large as the entire property or only as large as your budget will permit. If a physical barrier like a physical fence, that may stop some predators.......for others, it may not slow them down. Best barrier to slow most of them down is an electric fence, but that is going to require some effort on your part to maintain it.