The bear pit in Bern, Switzerland (Pinterest photo below) contains European brown bears and has concrete or smooth stone walls. Measuring the photo, the wall is about two times the height of the woman. If the woman is average height, the wall is about 3.3 meters to the capstone.
This question has changed quite a lot, so I will actually add another answer.
I can see the latest update for the planned Ha Ha wall as a workable idea, it seems to fit all the required parameters of your (updated) question.
However, the necessary height of it will essentially turn your outdoor campsite into a Vauban redoubt:
Here is a source for bear ...