I am going to assume that there are no minor children involved since you do not mention any.
These agreements are pretty robust because should he apply for any further provision the court will take into account that he is an adult and entered into the agreement (contract) freely. It is not possible to exclude the ability of the court to consider the position but they will only interfere with such an agreement in certain circumstances. Those circumstances are where one of the parties misled the other and has assets they did not disclose at the time the agreement was reached.The other situation is where something happens that may be beyond the control of both parties to radically change the position such as he loses his ability to work and you win the pools.As such you are pretty safe.
I hope this helps. If there are any further points please reply