Make sure that the security personnel have SIMPLE / CLEAR instructions on what they are supposed to do & how. This not only obviates errors, it makes it easy for the security company to ensure implementation of your orders.

The functioning should be SYSTEM ORIENTED and not people dependent.

Simply because it’s always better to use professionals for such a key and sensitive issue. 

It is also much more cost-effective to outsource it.

Also, would you rather not be focusing and concentrating your own work rather than be diverted by issues that you may not be best suited to handle.

A simple fact is that any fool can carry a gun, but knowing WHEN and against WHOM to use it calls for a high degree of intelligence and mental mobility, especially when confronted by a crisis situation. WHEREAS, most people, in a situation, which they VIEW, even remotely, as threatening, if carrying a weapon, are likely to draw and fire WITHOUT MUCH THOUGHT.

Also, an aggressor always has the advantage of selecting the time and place – hence, the gunman needs to be REALLY HIGHLY TRAINED & MOTIVATED to respond to it with accurate / effective fire. These levels of training are seldom achievable except in military / police.

The legal complications that arise in such a scenario are likely to be formidable and may cause more harm than good to the Principal employer AND the security company.

Hence, deploy guns around you if you seriously feel they are warranted and MAKE SURE that the legal aspects are taken care of.