To date, most of our vineyard is trellised with wooden posts - which has a major disadvantage when compared to metal posts: metal posts have "build-in" brackets that make it very easy to move the catch wires to a higher level as the grape vines grow and get longer.
Jeff decided to make his own system to allow us to move the catch wires: he cut metal strapping (the lighter weight, about 28 gauge) into short section, containing 3 holes. He then bent this short section into a U shape. He made a lot of them - coffee cans full of them.
To each U shape, he inserted a weather proof drywall screw and we screwed them onto the fence posts, about 6" above the fruiting wire for the first one, and the second one about 12" higher. Two on each side of every post. We used long, galvanized nails to closed the "bracket", to hold the catch wire in place.
It worked like a charm - we already moved the catch wires to the second level on nearly every variety.