Writing, signatures, disclosure, and independent advice for each of you.
To be binding, the agreement must be in writing and signed by both parties. Before signing, each of you must receive independent legal advice from your own lawyer about the effect of the agreement on your rights and its advantages and disadvantages, and each lawyer must sign a statement confirming the advice was given.
Both of you must disclose your financial circumstances fully. A court can set a BFA aside for fraud or non-disclosure, unconscionable conduct, if it was signed to defeat a creditor, if it's become impracticable to carry out, or if a material change in circumstances relating to a child would cause hardship. We draft with each of those grounds in view.