If you choose to free-range your flock, there are no guarantees of avoiding hawk attacks. I do agree with the above poster that having plenty of cover helps a great deal. Shrubs, plants, and different structures can offer quick places to hide. The decision to free-range should be measured with risk. Obviously, if one has a large flock that can handle the periodic loss then free-ranging may be the very best choice. If one has a small flock consisting of a dozen or less birds, then periodic losses can be devastating. It might be beneficial to have a fairly large enclosed run and offer limited, supervised free-range time. Since you have four pullets, you have to way the risks/benefits. (If roos are legal where you live, then it may be wise to add one to your flock. A good roo will offer good potection and alerts to his ladies.) -best of luck with your decision!