I'd suggest;
He move. It sounds trite or simple but sometimes, that may be best. As a security officer, I've worked in places where residents or visitors complain.
The managers or owners refuse to pay for security upgrades/improvements or they refuse to listen to security staff suggestions/reports.
Where I live is near the downtown area of a medium size city with a daytime population of approx 1,000,000 people. Crime isn't a major problem here but vagrants wander around often & thefts are not uncommon.
The property mgmt is lax about security & doesn't care about crime/safety.
They won't even install CCTVs or cameras.
If moving isn't a choice for your son, Id suggest he buy his own security system. Newer styles can be run with a smart phone or tablet. He can monitor his property & contact law enforcement/security if there's any trouble.
Buying a dog isn't a bad idea. Convicted felons & former crooks often say a loud dog or knowing a dog is in a home can be a serious deterrent.
Finally, if your son plans to get a firearm or a CCW, he should learn the local gun/lethal force laws. A pre-paid CCW legal service or a law firm isn't a bad idea either.
Crime prevention or safety isn't easy or simple but you can take steps to be secure.