Do you allow him to hunt your farm? If not, how big of a farm does he own and does he have crops on his farm? Maybe he is farming in a way that pushes the deer from your property to his. Or maybe the guy is busting his butt working in this poor economy and is just slacking on cutting your hay fields the way you like. I would say ask the guy what is going on with your hayfields and also mention that you really appreciate all of his help over the years. That should get a stress free, honest response.