Prenuptial agreements are an increasingly common part of American couples' wedding planning to-do list. However, some prenups won't hold up in court if challenged. You want to ensure to the best of your ability that yours will. One self-described celebrity divorce lawyer has some advice for how to "bullet-proof" your prenup.

Do It Early

Draw up your prenup at least six months before the wedding. The longer you wait, the easier it would be later for your spouse to claim that he or she was under duress. Once the venue has been rented and the dress has been fitted, you've made a big investment in the wedding. You've also told everyone you know. It may be difficult to refuse to sign a prenup, and you may not take the time to get the legal guidance you need.

However, the attorney notes, it's better to draft a prenup late in the engagement process than not at all. If you don't get around to a prenup, you can get a postnuptial agreement after the wedding.

Don't Include Unenforceable Provisions

Prenups are primarily intended to delineate how assets and debts will be divided in a divorce. They can make the process relatively conflict-free. However, there are things that they can't decide.

Child custody is a big one. Couples can't decide when they go into a marriage who will get the children in a divorce, even if the children are already in the picture. Child custody decisions under the law have to be made based on what's in the child's best interests at the time of the divorce.

Sometimes people like to include behavioral or "lifestyle" clauses. A common one involves adultery. If you want to include a clause that if your spouse cheats, you don't have to pay alimony, you can try to talk your attorney into it, but he or she will likely tell you that a court won't enforce that if your philandering spouse isn't willing to forfeit the alimony.

Be honest about your assets and debts. Some people try to hide how much money they have or how much debt they're in. Others exaggerate their worth. You shouldn't do either. Both people need to make full and accurate disclosures of this information. Failure to do so can invalidate all or part of the prenup.

Finally, both parties should have their own attorneys. Often one person's attorney will draw up the prenup and the other person's attorney will review it and recommend modifications. When people don't have their own legal representation, they can claim that they didn't fully understand the provisions of the prenup. An experienced family law attorney can provide crucial guidance and protection.