We had a bear prowl around a couple of weeks ago. It was most interested in the food (sunflower seeds) and carried off a half full 13 gal galvanized trashcan of it. And then it came back and lounged on our driveway. It didn't show interest in the coop or the chickens themselves, the seeds were outside the run/coop.
But I got anxious anyway and I bought the premier 1 42" high electronet and a very powerful energizer. It's not so much the netting that has to be strong, but the generated current has to be at least 6000 volts. Mine checked out when I had everything surrounded by it at 8000 with an occasional jolt to 9000. Don't skimp on the energizer. From googling the issue, while the bear was prancing on the driveway, I concluded that nothing short of a shock would deter bears unless you would build a concrete bunker with 12" thick walls and no windows.
If you want something portable, electronet is the way to go. If you can make it permanent (like a permanent perimeter fencing, it would be cheaper to go with 4 or 6 strands of wire and wooden posts, and the same strong energizer. We live on a mountain, so many rocks. I didn't quite fancy digging fence posts.