We have reached an agreement, now what?

We see a lot of clients who have gone through an amicable (as much as it can be) breakup and have been able to reach an agreement with their former partner with regards to splitting up their property and making arrangements for the care of any children. And this is a great outcome for everyone except when something happens and the agreement is not adhered to or someone wants to change things. How do you protect your interests once you have reached an agreement?