Additional
Didn't the ventian have two ltr based systems? Is it possible that they maybe on the other one? In any case I'm sure the stuff that is high security is done over nextel or a version simlar of nature as tobro or the old fashion call me at ext 2000 type thing.
Also, security as far as most people look at it don't realize this that its broken into two divisons.
Their is two version alone: floor security / hotel security, hotel security may consist of floor security and then their is corporate security that has more of an LP role (loss prevention apporach) surevilance control agents type sector. They may operate on entirily different platforms as far as radio goes, but share a common channel for take downs or interagency co-ordination concept.
More typical measure maybe appiled for corporate security aspect such as cell, blackberry especially or stuff that the ordinary public wold have. Do not be surpised if you see that one odd ball out like ie 800 mhz trunked system with a vhf frequency on another license to the casino. That vhf frequency that does not seem to fit might be a invetsigate type channel for onsite activities. Bascally hidding in the obivious is the concept, you may even hear activity on lvmpd tac releated channels or their trunked systems depending on the alliance or interagency co-operating capabilities.
Its not like its some small deal person with no money to spend on technology, massive bo ko bucks here for technology and if their is a cheap and effecient way you better beileve they have look into. Think simple first, if it works and no one can hear it or limited people can here your all set. Simplex is good for this as well.
Theory 101
I have a pair of frequencies that operate on 152.0000 tx and 157.0000 rx for a repeater. I now have just created 2 more simplex channels that a license will support. Not to mention all the digital modes that exist and pl/dpl. Then I have a few more options to play with, murs channels. While low powered and open to everyone then comes the usage of codes or phrases are what you really are listening for. That could very by property. The other traffic your hearing is open mode type things, things they want or now you can hear with in reason. Granted an emergency is not going to be secured unless operating naturally in that mode already.