Here’s how we have worded it: “All guests have to be registered. The reservation should include the total number of guests – max is 4. Exceeding agreed-upon guest reservation is cause for cancellation and removal. Visitors are not allowed unless pre-approved by Peggy and Mike.”
Because we are on site hosts they can’t slip people by, but we have found that people feel like they can just invite anyone up for the day or to come on over if they have local friends. This wording has helped uncover those circumstances and we’ve been able to manage the times where it was okay and some where it was not. We also added (after reading this forum) that breaking this rule is cause for immediate cancellation and removal so the consequences are clear.