Invest in some reeeeeeely good locks, keep track of the keys (don't give everyone on the planet one). Subscribe to a burglar/fire alarm service (so you don't have break in's and a fire that "smoldered for several days before it went up" and arrange to have the property checked every so often----many times these restoration projects are away from where the main group is and people only show up once a month or so to work, having someone drive by every couple of days and at odd times can help keep bad guys away.