Can I really prevent my ex from joining a club/society I'm a part of?
why do you want to prevent your ex from joining your club?
Because he often disparages my clubs when they're in any way connected to me, and I want to prevent that from happening.
I understand that you want to avoid your ex especially when he denigrated the club just because you were part of it. Although I doubt you can prevent him from joining the club. You better leave him alone.
Okay, I'll console myself with the delusion that I have control over who gets to join the club.
They're your ex now so it's not in your hands what he does in their life.  I understand you don't want to be around them anymore.