Consider having it a ticketed event, even if you want to keep it free of charge, through some form of prior booking or reservation. This takes more work to organise, but it allows you to screen out people you know who have behaved destructively before.
Control access through designating who is admitted: 'students of this university only', 'members of the Islamic Society only', and so on and make sure this is on the publicity information.
Have it invitation-only, even if the invitations go out widely.
If it is a small event, circulate your principles or policies beforehand and make sure everyone agrees.
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