How does a cultural institution with limited financial resources provide adequate security protection?  One idea is to look for synergistic "force multipliers" to augment your security staffing. 

The groundskeeper who spends his/her day maintaining the landscaping is extremely knowledgable about the normal activities that occur on site. Enlist grounds staff to alert you if they see someone acting in an unusual manner, for example, if they see someone taking picures that visitors don't normally take or they notice someone sitting in a car watching deliveries come and go.
 

Volunteers who staff the information desks or assist in wayfinding are also good candidates.  Teach them to report unusual behavior such as visitors who ask questions about the number of security guards, or visitors who wander off of tours, activate emergency exit doors, etc.

We know that most terrorist attacks involve advance planning and "casing" of a target.  By training a cross-section of staff to look for suspicious behaviour, we can increase the probability of discovering or deterring a potential attack in the early planning stages. 

Developing an institutional mindset that "security is everyone's business" will go a long way towards safeguarding your visitors, staff and collections.