I have seen this type of problem solved very effectively after a certain persons wife and daughter were threatened.
To me threatening women and children is a deal breaker for me and one should not take prisoners.
We all know that these deadbeats have no respect for law or authority and think they can do what they like with impunity.
So a couple of gentlemen in balaclavas paid them a visit, kicking in the front door and trashing the place.
No mention was made of why or what for, except that they were advised to move on or next time it would get a little bloody.
They would suspect one of their deadbeat mates or possibly an unhappy customer or dealer.
On leaving a few windows and walls were a little destroyed, just to make the place comfortable.
They called the cops, and the cops asked if this person if they saw anything and this person mentioned that there were a lot of druggies hanging around all the time, which ones did they want to know about?
This person could honestly say that he had no idea who did it, as they had balaclavas on.
Long story short, they left, cowards who threaten women are not brave enough to stand and fight.
I am also aware of another time when problems were solved without bloodshed.
At a certain beach side suburb, a couple of fly in louts were stealing, bashing and generally threatening people in the area.
A group of men got together and grabbed the louts, bundled them into a RIB and headed off shore some miles.
Reaching a suitably distant location they tossed the louts into the drink and said that they could swim back.
or
They could leave the area immediately.
On the way back to shore they were advised that next time, they would be taken further out and left there.
Result, they packed up and left that night.
Problem solved
Cops have to work within the law.
These type of people know the law, their rights and how to abuse them.
If someone has no respect for you or the law, You need not show them any respect, and the law will protect them no more than it protected you.
The only way to fix these issues is to work outside the law, as they do, and let them know that it will not protect them.
Just be sure that they dont know who it was that did the deed.