Wow! Does your friend (his wife) know he keeps coming by you?
It may help if she does, you did say their marriage is rocky, she, in some indirect way may be able to go to the police and help convince them that he is a problem, and really is stalking you, etc.
It's so hard to believe the law(s) would allow someone like him to continue to harass you and others.
That stinks, and is not fair. See, if there is something more that you can do, you need to protect yourself from this deranged man. Sounds like the police there are useless, maybe if more than one person goes and talks with them, you'll get more serious attention?
I wish you lots of luck and safety with this matter.