|Strawberry inspecting the frost, Nov 2017|
As you can see from the photo, I've enclosed their section of the lawn fully using chicken wire and a selection of poles; they have a strip about 2 feet wide by around 12 feet long (ish). I move this piece of chicken wire across the lawn every two days: it's attached to their permanent run at the back of the garden. They've already made two passes from one end of the lawn to the other, and will possibly be able to make one more this winter, depending on the state of the grass by the time they finish their current pass.
Those two escape artists still manage to jump out most days though. I can't think of any cruelty-free methods* to stop them; they're the two best egg layers--actually pretty much the only layers at the moment--so I can't even justify making chicken stew...
*I was thinking maybe a reversible one-winged chicken strait jacket; one wing gets pinned down, but it can be swapped over so she can still stretch and groom each wing. Probably not RSPCA approved though.