Equipment can be rented. Adjourn in time to allow members to do their independent work, eat and rest. Begin to pace yourself and the Board. Tactfully, but firmly, dissuade visitors regardless of rank. Most people are deferential to uniformed personnel and respectful of roadblocks, gate guards and a marked perimeter.
Some people require reminding.
Site guards will take your lead. Be prepared to back them up, because there will be requests for exception. Requests will come from press, government functionaries and military personnel who drop by. If the visit has merit, provide escort, keep it short and do not disclose privileged information. If someone's purpose is eyeball liberty, let him to do it outside the perimeter.