Here' s a little trick I use in putting wire on trees. I put a treated 2X4 on the tree using two large spikes and use that as a base for mounting the wire. That way the tree cannot grow around the wire. And it' s possiblwe to remove the board and nails if you take the fence down. I think I remember you saying that the farmer has had timber cut in the past. If loggers cut trees with metal in them they can get very upset as it can ruin a saw blade when cutting lumber from them. I have heard that in some cases they have come back on the owner. When I had Pines cut last year, I marked trees that might contain metal for the logger.
Russ