An active build is open in ways a finished building is not. Fences move, gates change, and equipment and materials sit on the ground overnight. Most theft and trespass happen in the hours nobody is there.
The gate
Every person, vehicle, and delivery that enters should be checked against a list and logged. A staffed gate is also the simplest deterrent a site has.
The perimeter
Rounds on a set schedule catch cut fences, open gates, and damage before they become losses. Each checkpoint should be logged with a time.
After hours
Sites that close at night need either an officer on post or a patrol that checks the site on a schedule and responds when an alarm trips. Many builds use both at different phases.
Change coverage as the site changes
A build at excavation needs different coverage than a build at fit-out. Revisit the post orders and staffing whenever gates, hours, or the value on site change.