When someone sues your spouse or your partner, your property may be vulnerable if the suit goes against the defendant. It depends on a bunch of things, including state law, when you bought the house and the reason for the legal action. In many cases you are protected if you bought the house with no help from your spouse and the title is in your name alone.
In the nine states with community-property laws, most of what you buy during the marriage, including real estate, is your spouse's property too. If you bought your house after tying the knot, legally it's half your spouse's; anyone with a court judgment against him can put a lien on it. If you acquired the house before your spouse, it's yours alone and safe from his creditors. You're also not responsible for judgments stemming from debts your spouse rang up before the marriage.
In common-law states -- the other 41 -- marriage makes you one flesh but not one income. If your name is the only one on the title, it's your house - 100 percent. If it's in both your names, it's shared property, even if you pay the mortgage. Creditors can't go after your personal assets unless state law specifically allows it. In Minnesota, for example, you're liable for your spouse's medical debts.
If you worry about your spouse -- say, because he has a pile of unpaid debts or is in a business with a high risk of liability lawsuits -- a prenuptial or post-nuptial agreement is one way to protect yourself. The agreement spells out that you're not merging your finances and anything your spouse owes is his responsibility. Then make it a point to shield assets from potential lawsuits. For example, buy the house solo if you can afford it.
Even if you're legally free of the debt, whoever secures the judgment against your spouse may try to collect from you anyway. He may inform you that if you don't pay, he'll apply the lien, either because he doesn't know the law or he's attempting a bluff. Inform him you're not going to pay and the reason why. If you're not legally responsible for the debt, don't pay. Do show up for any court hearings or dates so you can tell the judge why a lien would be unfair. Failure to appear in court when summoned can result in a judgment in favor of the plaintiff.