I would build a run for when you are not there to montior the free ranging. And monitor them when they are out. I had chickens free ranging for a long time, with no incidences, but then came the fox. I thought all I had to worry about was night time predators and hawks during the day. well, it turns out fox are crepuscular. that means they hunt for 2-3 hours surrounding sunrise and sunset. So I leave for work and mrs fox comes and eats/kills/chases away 8 chickens somehwere around 8-8:30 in the morning. I hear that if you have dogs and they can stay out all day with the chickens will protect them from such things, but idk personally. My dog is a total wimp and didn't even realize a few weeks ago that the fox was standing 15ft away from her.
Like I said, I used to free range and they had free ranged for a few months, with no monitoring while we went to work and what not. But I had just got them and the predators were unaware of their presence. Built runs for them cause my DH was mad that they ruined the landscaping he did, they were in runs all winter. Then spring hit and we built a new coop and since we weren't done with the runs, I let them free range all weekend. So that monday I thought "my biggest worry is loosing one to a hawk" and they are so good about hiding from the hawks. WRONG! at 12:30pm when I came home and was missing 8 chickens. only 1 returned.
so, if you love you chickens like I do, avoid the despair of coming home to find dead/missing chickens and build a run. I always felt bad keeping them in the runs, but bored chickens are way better than dead ones.