Mountain Stance gives, among other things:
you gain a +4 item bonus to AC and a +2 circumstance bonus to any defenses against being Shoved or Tripped.
Some creatures, like a wolf, have the knockdown property.
As I read the rules, Mountain Stance wouldn't provide any benefit against knockdown. One of my player is a bit frustrated that his features supposed to protect him against being tripped (as encountering creatures with this feature has been more common than foes who use the Trip action in my campaign so far).
Do you know of a house-rule (or an official ruling if I got it wrong) that would help?