Your question brings up another question. Inside or outside the fence?
We will soon be getting our LGD's. We are opting to "not" have them fenced in with our animals, but rather to have them outside the fencing with the ability to patrol. This is why we are going this route:
It is my understanding that it is instinctual for the LGD's to protect and stay near their charges. As long as they have enough to do and enough charges to watch over, thus keeping them busy, they shouldn't really have a need to wander off. The LGD's are supposse to warn off predators that they hear and see from a long distance away. First by bark, then bark and run, then kill if neccessary.
If they are on the outside of the fencing, they have the ability to do all of the above. If the LGD's are on the inside of the fencing, they have to wait until the predator is within the fencing where your livestock is in order to charge and or kill with any effectiveness. We want our dogs to be able to chase them off long before they get in sight of our livestock.
I believe that each situation may be a bit different. We have 26 acres that are not completely fenced, but our livestock fenced in a smaller acerage within the 26. We then have hundreds of acres behind us so if they do roam in order to chase predators away, I am ok with that. If we had a small amount of land, we would most likely consider fencing in the entire area.
I think a huge consideration is having enough to keep the LGD busy so that they don't desire to wander. They are working dogs and desire to work.