Get a realistic-looking bear cub stuffie, and stick into it a Bluetooth speaker that is playing a looped recording of a cub squealing in pain/terror.
Make sure to carry it in your hand, or on the outside of your backpack, because it only works if they can see it.
That way they'll know that you're a dangerous customer, and not to be messed with.
But for generally keeping them away from your camp site, nothing works as well as: