I’d think cameras would make them think twice! Though then you have to watch that they will perhaps try to work out of sight to them, but it would be so with a guard as well. Also depends why their motivated to get in, if its something inside locking it up and making note of that could stop it, if thats possible. Windows would be my major concern as a hazard, especially if they think their out of sight. Other areas they could get in like that would also be a concern. be sure to check any methods of entry for concern, if theres areas they could climb to get on the roof, or in other windows that should be considered too.

If you have the funds and labor available, you should fence it 10-12 ft high with razor barb on top.

you build a 12th century style English moat around the entire facility

Hire an onsite guard!

have security/police on site every hour! Have them rotate every hour!