My kids are lucky (although I doubt if they would agree with me). Their dad and I have, since we divorced, communicated and backed up each others' discipline choices. If one kid is grounded at my house, he's also grounded at his dad's. And they know better than to ever try to play one of us against the other (as in, "Dad said it's okay with him.") I just pick up the phone and call dad to check, so they know they're busted if they're not being totally honest with me (and vise-versa).