Religions also draw up marriage contract, some terms need to be set or its a free for all like we have today with the gays and other wackos. With all kinds of free lancers and wise guys who think they can do a better job inventing the wheel
Here is the Jewish marriage contract http://en.wikipedia.org/wiki/Ketubah Which among other things sets out the responsibilities of the husband and protects the wife
The key word is contract. Either religious courts or civil courts end up having to enforce it. So no matter what you do, some third party authority ends up having to enforce its provisions.