Hi some good answers others not so good.
Get the business owners together and see if they want to hire a security guard. Start with that and see where it goes. You have already done other things I would check that one out.
It is the sign of the times, probably a write off other large corps do it and you know they go for the most write offs lol.
Landlord should be held accountable, also he might help with expenses.
My friend owns a large working complex. Tall fences and a gate that locked and keys for the renters. But I would try the security angle first. Lots of lights and security drive by is good or it could even be more intense, Pocket book is to be considered but split 10 ways (others) it might be OK.