Spouses that lie or under-report income are not uncommon in Divorce and Child Support proceedings. You have to bring whatever evidence you have of the under-reporting to the court’s attention. You should file a motion for further financial disclosure, which opens the door for a discussion of his finances in court. You can also use evidence of a life-style inconsistent with his reported income as evidence of under-reporting.
Hiring a private investigator or forensic accountant is another way to expose under-reporting. Where the conduct is egregious enough, I have reported lying husbands (and wives) to the Internal Revenue and forced an audit, letting lose the forces of the federal government to unearth the hidden money. Facing jail, heavy fines and penalties, most spouses cough up the money. 🙂