Our children always disobey when we have a babysitter. how do we get them to obey our rules when we leave?

we have three children, 6 1/2, 5, and 3 years old. when our babysitter comes over, our rules go out the window. our children know what the rules are and what we expect of them, but when we leave, they try to get away with as much as they can. i understand some of this is normal, they are kids after all. we have left a list of "house rules" for the sitter. these are things that the kids have done when we aren't around and we have found out about after the fact. after she's been made aware of these rules, they have been obeyed. but, then something new comes up and there's another thing to add to the list. but, when it is blatant disobedience, what can/should we do? will there be a time that the children obey our rules when we aren't home??