I think I may be giving the wrong impression. I keep restating that I will not keep allowing them to go into the neighbor's yard and if need be they will be cooped all of the time.
However, I disagree that this will definitely not work. Does it have a possibility to fail? Absolutely...overwhelming in fact. But I have read accounts of people training their birds to stay out of certain areas. In fact, there's an area of the yard that the chickens previously loved. But too many times of the dogs chasing them out of that area has resulted in them not going there at all anymore. We have tons of green land with trees, bushes, etc. So far they have not explored that area.
Also, maybe I didn't make this clear, but currently the chickens spend the majority of their day in the woods or other parts of our yard. It seems to be the 30-60 minutes prior to dark when they enter the neighbor's yard. So it will not require me standing out there 24/7 to keep them out of the neighbor's. However, as I said, if it does not work (and you are right it has a high probability of failing) then they will be confined to the coop (or a tractor).
Also, since this just started happening, I don't even know if the neighbor's actually mind. (Don't worry...I'm not going to assume that they don't and continue to allow it to happen). We live in a small country town where lots of people have chickens. Everyday I see chickens in yards that are not theirs. I plan to apologize to them this weekend and tell them my plan and that it will no longer be an issue (I don't even think they've noticed the chickens in their yard). Maybe a miracle will happen and they'll say it's fine!