I was thinking barb wire, too. I need to do something because I bought a lot of my fruit trees fall of 2019 and so they should be producing next year and they’re pruned low, not to mention I upped my berry game this year.
Not barbed wire: high voltage electric fence wire. Run a single strand near the top with a charger (you can get solar powered ones if there's no AC nearby) and that will stop them in their tracks.