What can u do to get out of a business or protect youself from someone else debts?

My fiance and his dad own a business building together. His dad runs and owns the business which he has taken on some debts doing so. And a lien of his dads popped up out of nowhere against the building shortly after they put it up for sale. So does my fiance now haveto suck it up because of someones elses mistakes? Sure they could have had an llc partnership but my fiance only owns part of the building. What could be done in this situation? Will my fiance be responsible for all debts owed on this business and building if something would happen to his father? Could he some how protect his portions of his investment or is it to late??