Carl is the network administrator for a large stadium that hosts many events throughout the course of the year. They equip ushers with handheld scanners to verify tickets. Ushers turn over frequently and are often hired at the last minute. Scanners are handed out to ushers before each event, but different ushers may use different scanners. Scanners are secured in a locked safe when not in use. What network access control approach would be most effective for this scenario?