A few things for you to bear in mind: It's not clear from your question why your ex-husband owes you this money. If it's for a child support or spousal support judgment, then he cannot get out of owing you that debt even by filing for bankruptcy. Domestic support obligations are explicitly exempt from discharge under bankruptcy laws.
You can't stop him from filing for bankruptcy. But if he does, then even if the debt he owes you is subject to discharge, that doesn't mean that bankruptcy will let him keep all his property and avoid paying you. If he files for bankruptcy, he'll have to either liquidate his property to pay back his creditors (including you) as far as possible, or set up a repayment plan. You can appear in the bankruptcy case as a creditor and argue for why your debt should be granted higher priority than others.
There are steps you can take to seize your husband's assets directly, to satisfy your judgment. A judgment with a money order can allow you to garnish his wages and bank accounts.
To evade such garnishment, some obligors will only work "under the table" and for employers who they think will refuse to comply with the garnishment. Doing that can have serious consequences to the employer: They can be personally liable to you for the debt that their employee was expected to pay. But if you're dealing with a private person who doesn't understand their responsibilities as an employer, this may be cold comfort.
You can also seize bank accounts directly. You must have specific information about your ex-husband's banking institutions to do this. If you do not know this information, you can have him served with "debtor interrogatories" or compel him to appear for a debtor examination. This is similar to a deposition: it is an interview, under oath and before a court or a court reporter, where the debtor must answer questions about their assets. You can use this information to attach those assets and get repaid for your debt. Failure to appear or answer is punishable by contempt of court.
There are several potential problems, though: supposing you do prove to a court's satisfaction that your husband has income and has refused to pay you, the judge will order him to pay as the judgment says. If he fails to do so, you can seek an order for contempt. You can ask the court to order him to pay your attorney fees, or in an extreme case to put him in jail if he's willfully refused to comply with the order. This last remedy is very rarely ordered, but it can be appropriate to request in an extreme case where an obligor (person paying support) repeatedly and intentionally refuses to comply.
However, putting him in jail wouldn't put money in your pocket. The law can't technically "force" anyone to do anything; it can only impose penalties for not doing so. If your ex-husband is really willing to incur those penalties - if he's really willing to go to jail rather than pay you - or if he can persuade the court that his failure to pay was not intentional so he should be spared that most extreme of sanctions, then there may be nothing you can do. This is a recurring problem for creditors: having a judgment only gives you assets if the debtor has assets to take. When you've got nothing, you've got nothing to lose. I don't know how far your husband would be willing to go to avoid paying.
Ultimately, you may need to find a way to survive without your ex-husband's assistance, even as you pursue collection from him. You should consult with an attorney in private if you want to pursue collections in this way - the process is complex and you can't expect to navigate it on your own. There are strict requirements with which debt collectors must comply.
