The more sensitive your event, the more you should consider the entry or admittance protocol. For high-security events, be sure to include on your invitations the mode of entry required. Don’t skip on any details around guidelines, such as bringing the physical invite to the event, or RSVP’ing at least 24 hours before the event. Even if your guests can bring a plus-one, you can require the plus-one to be added to the official list well in advance.
Feel free to require ID at entry, and to provide some type of visual proof of validation—such as a stamp or bracelet. But just be aware, a stamp or bracelet may not suit black tie and formal events. You should also have a secondary system in place for screening your event vendors. You should make it easy for the catering team, lighting and sound, A/V, decor, entertainment, and anyone who has access to the venue during setup or the event, to come in and out. Be sure to also communicate the protocol well in advance to your vendors.