I use direct booking for my short-term rental, but also several channels like Airbnb. With direct booking we have a security deposit that places is a hold on the guest credit card until after they leave. However, with Airbnb you have to go through their channels to collect any kind of damage fee. For that reason, we have a pet policy that a pet has to be 20 pounds, housebroken, and crated when they are left alone. 
A guest recently made a reservation and then told me they will have to bring their dog with them. He claims that the dog is housebroken but it is a three month old puppy. He also claims it will stay in the crate and even though it is a golden retriever it is not yet 20 pounds. So technically, according to him The dog meets all the requirements for our pet policy. I don’t feel like I can tell him no, but I would like for him to sign some kind of agreement or do something to make a security deposit for potential damages. Is there anyone who has done this outside of Airbnb? Like send him a separate document to sign?

(obviously I will be adding to our pet policy that the dog has to be at least two years old or something like that.)