First of all, I am not talking about Black Bears. I've dealt with Black Bears and they don't worry me that much. I'm only talking about Brown Bears, commonly called Grizzlies in some parts of the U.S.
Previously when in Yellowstone and Glacier Parks, I was prepared with either Bear Spray or a Bear Flare or both. I only saw two Grizzlies during those visits. Since I drove there, I could transport either device in my car or attach either to my belt. Not a problem.
This year I will be visiting some other national parks with Grizzlies. Unfortunately, I am flying there, and that rules out transporting my own Spray or Flares. In some instances, I could keep purchasing new Spray or Flares, but then I would need to get rid of them before flying home, assuming that they didn't get used. In other instances, I won't even have any opportunity to purchase Spray or Flares.
Now, in the parks, you can't hunt the Grizzlies anyway, so forget about that.
The general advice from the NPS rangers is to walk through the backcountry in small groups. Unfortunately, I will be alone. NPS tells you to make lots of noise to warn the Grizzlies that a human is coming, because it is mostly the surprise situations that get really ugly. So, NPS tells you to talk or sing. Boy, that can get old.
I suppose that I could bring a whistle, but I'm told that whistles are not as good as a loud male voice.
Then I thought about one of the small air horns. There are some that aren't any larger than your hand, and they are transportable by air. I wonder if that would halt a Grizzly charge. I have some doubts. The whistle or voice could warn of my approach, and then the air horn might do something in the event of a charge.
When all else fails, you drop to the ground, cover your head and neck if possible, and play dead. NPS says that often a charging Grizzly will run up and stomp on you, and then walk off.
I ask, what is a good ultralight Grizzly bear repellent? I will rule out sheets of titanium.