@Dave45
It's not possible to implement a security deposit retroactively.
You'll have to sweat this one out 😉
Anything you add to your house rules though, as far as I have learned, still have to be respected.
You might want to add something about loud noise if you think it's necessary. Or if only booked guests are allowed on the property and whether disregarding this would lead to immediate cancellation.
If they still cause you to be nervous, think of any other drama that could arise and adapt the HR accordingly.
In case your guests are still unruly message them on the message thread (important to keep a paper trail for Airbnb, possibly even refer to the first disruption too because Airbnb will use this communication as proof in case of any problems or complaints by guests).
And do know that this community forum is extremely wise reading to build host muscle. Hosting is not for the faint of heart!