We have a small retail strip in Tampa.  It has been a real challenge because of the homeless.  It is actually in a decent area, close to Carrollwood, but it is also close enough to suit case city that the homeless can just walk to the property.  It has become a favorite stopping point, b/c there is a Dunkin Donuts on a shared outparcel.  They dumpster dive at night and get donuts and bagels out of the bin, bring them over to our strip center and have a party.  You can imagine the mess left there every morning.  They also intimidate the hell out of the tenants, most of which are office workers.  

Human security is very expensive and the size of the property does not warrant the cost.   Alarm companies are not allowed (by regulation, apparently) to put alarms on the outside.

I am thinking about getting a motion detector and install an outdoor speaker myself, with noxious noise.  If they come underneath the over hang, the noxious noise will start playing.

 We have tried everything...from asking them nicely, to calling the police (the police won't even come out any more for the homeless calls) and leaving a barking dog in a vacant space at night where they like to hang out (they just move away from the dog and find another cozy spot).  

Does anyone have any suggestions?  It is killing occupancy in the center.