I think free range chickens learn how to avoid hawks given time. The learning process can be painful, and there will be losses. If your chickens are pets, and you only have two, I don't think letting nature run its course would be a good idea. I think that in your case, you will have to go with a tractor or some kind of netting.
Things that I think work with hawks if you can take some losses while the chickens figure out things:
1. rooster(s) - they are more vigilant than hens. They are bigger, have spurs, and some will even put themselves out as decoys to let hens reach cover. My hens head for cover when the alarm goes off, sometimes there is a straggler separated. I've seen some roosters that will go to the hen, across open ground, and escort them to the others. But it is a somewhat rare trait.
2. bird feeding - encouraging song birds to be around all day (and squirrels) is helpful. They look out for hawks and raise an alarm when they spot one. The chickens can learn this alarm and head for cover. They become part of the neighborhood hawk patrol.
3. Move your waterers - if you have water outside for free ranging birds, move it around and keep it near cover. If hawks see chickens coming to a waterer enough, they will use it as an ambush site.
4. Cover, cover, cover - if you don't have large bushes or man made things to hide under, they are sitting chickens. Chickens don't seem to run back to the coop as a first choice (probably because the small door won't let them in all at once, or it is evolutionary to draw the hawk away from laying/roost sites). But under a deck seems to be a great hiding place (I've seen rare instances of hawks diving into bushes to scatter flocks, but never into a house or under a deck).
I've been free ranging for 30 months, I've only lost birds when:
1. they were young and inexperienced
2. I had no roosters
3. I had neglected the bird feeders
4. I had become routine with placing my waterer in the same spot, between, two bushes