A physical barrier, then a wide landmine field, a 2nd physical barrier, then a road, then a 3rd physical barrier. Small bases for military personnel to perform regular, but random patrols. Anyone not US military inside any of the physical barriers is shoot to kill, don’t bother asking questions either before or after. Sensors for tunnels, coverage for air incursions. Use the Korean border as an example or even the East/West German border.
That’s remarkably close to my idea for how to deal with Detroit. They lost some much population that the city needs to physically downsize. I recommend that they make several large multi-square mile no go zones. These areas are clearly marked and fenced with a single strand of barbed wire. The land will then be leased to police, military, fire departments and anyone else who needs an urban training ground. Fire can burn at will. Police and Military can have all the shoot houses they want.
If you get caught in the no-go zone, be prepared to die. You may be caught in crossfire, you may get shot, you may survive. You will not be treated or helped in any fashion.
After a year or two, most of the homes will be destroyed and partially demolished, making it easier for the city to finish the job using money from the land leases.
The land is to be made fallow. All infrastructure, including sewers and basement are to be removed, rendering the land ready for farming and/or future development.