We've had chickens killed by animals that dig below the fence and by animals that climb over it and by birds that fly over it. If you cover those areas then yes they won't die, chickens are pretty sturdy. Or you can just buy/breed new chickens, it doesn't happen that often (may depend on your area though). One of the hens laid beautiful light brown eggs with a pattern dark brown dots. Sadly she died to a marten or fox.