Sifers$-$Grayson needs to improve the physical security for its test range where operational and experimental tests are conducted for both robots and drones. The test range is located in a sparsely populated mountainous area approximately $25$ miles away from the company's R&D center. The company has an agreement with the state police for pre$-$arranged $($scheduled$)$ closings of a nearby scenic overlook which lays within the approved flight paths for drone testing. The test range property itself is enclosed by $12\text{'}$ fencing topped with barbed wire to keep unauthorized individuals from entering the test area. Which of the following additional physical security measures is most likely to provide the company with assurance that intruders cannot enter the property unnoticed?

Question $43$ options:

Electrify the fencing and post warning notices to discourage attempts at unauthorized entry.

Establish a no$-$fly zone over the property to prevent access via plane or helicopter.

Install motion sensors around the fenced perimeter and tie them into a $24$x$7$ central monitoring service $($responsible for notifying key personnel and emergency response services$).$

Hire a guard service to provide an onsite guard who is responsible for monitoring the gates and walking the perimeter on an hourly basis. Guard service to provide one guard per shift with $24$x$7$ coverage.