Sandy, off-duty police officers are definitely a benefit onsite for the performance of securing your property. For a really problematic property, I highly recommend hiring off-duty officers who are familiar with your property, its particular challenges and who have a relationship with the law enforcement agencies. They are no more prone to hitting and bullying behavior than some "Rent-a-Cops" who strap on a gun and walk around thinking they are one impenetrable defender.
However, the caveat is this: who you hire must respect your community's rules. They are there to check the property, buildings, parking lots, and common areas. They are not there to sit in a parked car somewhere on the property for 20 minutes with a revolving strobe light on top "warning people security is present." They oftentimes will fall asleep or simply "check out." Those security "guards" do not Guard at all. They are a waste of money.
You have to know what you want before you can find the right person for the job. Trust me - a lot of companies who offer "paid security guards" often hire pretty much anyone and don't pay much. That is why there is so much turnover in that industry. So, beware and set the schedule for what you want. I used to go to the property at midnight, 3 am, and every time in between. NONE of the security companies were any good and I ended up working with police back up and patrolled my own property myself.