This is entirely up to you. It is perfectly reasonable to ask your house sitter for a security deposit to insure against any damage to your property. If you would prefer the peace of mind a security deposit can bring, make this clear when you first contact potential house sitters. The amount is negotiable but shouldn't be more than the equivalent of a month's rent for a similar property in the area. Our house sitting agreement has a –security deposit lodgement' form included in it which you can use to help make the whole process more organized and straightforward.