Some birds do range out pretty far. If you feel it's dangerous, you may need to fence off an area instead for them. Mine were huge on wandering and with the mountain lions and coyotes, I felt they would be safer behind a fence. So we put up a 100x100 ft fenced in area and they stay safe.
Hello and welcome to BYC. My chickens are free range, but they stick pretty close to home. If yours are roaming too far I would suggest keeping them fenced in.
are they young or new to the area. If so they might be wandering and stop after they associate home base as the hen house or you could have a wandering problem
We have always free-ranged, and they inch into the farmer's fields next to us, but that's not so bad. After it rains, they go out to the tar road for worms, and whilst we don't have many cars, I still go herd them in. Have you tried repeatedly herding them back? These are silkies, and if they can learn any chicken can.
I free range my chickens, but in a chain link fence so I don't have issues with roaming. I used to have some chickens fly over the fence though and roam around, but it's not a problem for me anymore.
Your flock is probably curious, so that's why they keep roaming further and further away. The only way to stop it is to put a fence up.
Good luck!