Unfortunately, that is also the law in Maryland. My exAH refused to sign the separation agreement. I didn't want much, but he was unwilling to give me anything. At the end of two years, he was served with the divorce complaint, which he signed. It was a moot point by then because after two years, I could be granted my divorce.
Is there any chance of renegotiating the settlement so you don't take a major hit, but can throw him a "bone" that will get him to sign?
The problem is, that as more states become no-fault, having a drunk or a druggie in the home isn't grounds to get a divorce. HOWEVER ... Laurie makes a very good point. The guy is being a nuisance and endangering the wellfare of children.
Have you considered a restraining order to get him out of the house? It would be worth your while to investigate that option.