If you mean free range as in "not fenced at all", that probably does not work, unless you have a lot of excess food/space for the number of chickens, and no predators. Or, you give them plenty of forage, including forage beds and forage trees, and fence them OUT of the gardens. But chicken foraging (perhaps all foraging) works better if you have the forage divided into sections so that you can run the stock on one section while the other sections recover, then move the stock to a new section and let the section they have been on recover.
They will certainly climb, and dig. Given
enough (or too much) time they will destroy (if you mean dig up all the plants) and scratch down a lot of the dirt. Given less time, they will simply go though and start on the easy pickings, but they have either no idea, or a very specific idea, of what you don't want them to eat, and will start with that if they can get at it
so you either don't let them at whatever you want to save from them, or you wait until you don't care about it anymore before letting them in.
Having done chickens in the past, I see advantages to plain old rectilinear beds that are easily enclosed in a temporary/mobile chicken cage if you want to have the chickens work parts of the garden.
Have seen some round versions of such cages, but having gone through several iterations of bed shape/size, with various theoretical foundations I look at the "keyhole beds" and think "yet another thing that looks great in computer graphics, and likely works (and looks) not so great in my garden" - YMMV.
With 10 acres, is "relative amount of path to bed space" really a top priority in your garden? While I realize that everyone prefers what they prefer, and no doubt people who love their keyholes will come crowing, I find that I can much more effectively work a bed I can easily straddle, rather than standing in a spot and reaching into it. I'm also less than convinced that the entire garden as a whole ends up with less path to bed, as generally implemented. Could be you just like the look of it, which is fine, and a better reason, but it may make managing chickens in there more complicated (or very simple - let them into the whole garden in the spring, then fence them out until after the last fall harvest (or at least until you fence off individually the last few things you are harvesting in the fall.)
I'm coming down to 30-inch wide beds (75cm-ish) After having started at 60 inches (I can reach 30 inches - I measured it! Hmm, this is harder with plants in the way. I can't actually pick the stuff in the middle. Wait, I lost my balance and stepped in the bed - I'm not supposed to be stepping in the bed.) Revise to 40 inches, repeat, revise to 30 inches. Now I need to re-layout the garden next fall with adequate paths, as they got shrunk when the 30 inch revision went through, and some of the 40 inch beds are still there with things that will need to move, eventually.
I also moved away from "very long beds" to much shorter beds (currently 6-8 feet - 2-2.5 meters) because the long beds were harder to compartmentalize for weeding, etc. - less path space, but mentally (and thus practically, as the mind has to manage to deal with the work that's to be done) problematic. More paths and "manageable" size works better for me in practice.
Am closing on 10 acres at the end of this month, and have been digesting books and videos on permaculture design for the last few months.
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