Here's the thing I don't really understand about the concept. In my garden anyhow, the great majority of troublesome plant pests FLY in, and then (most of them) reproduce ON THE PLANTS.
Chickens will help very little with the flying-in part (only if a particular individual bug happens to get caught by a chicken on its way through the 'moat', which seems like it would most of the time *not* happen) and cannot help at all with the reproduction-in-situ problem.
So I am not getting how it would do any good with most of the biggest pests, like aphids, any kind of caterpillar (hornworms, loopers, borers, etc), mexican bean beetles, etc.
On that BYC thread, the only person reporting having done it and having had some success was ALSO letting the chickens INTO the garden to clean up pest problems as they developed. And the MEN article only reports success vs grasshoppers.
Not that discouraging grasshoppers is *nuthin*, but I have yet to see anything to convince me that it's worth the considerable extra aggravation and expense, unless one just wants to do it as a Fun Idea.
I think that is a great idea, if your property lends itself to that kind of setup... I have my chickens on one side of the garden and I really do think it helps with bugs, etc. I think you could do this without too much effort, if you were only going to have the chickens outside with you, when you were in the garden... Not worrying about predators, etc. When I am working in the garden, all my chickens stand around begging for weeds and goodies!!