I've actually had to deal with this before. One of the biggest problems is that you have a gun readily available if you are terminated, get pissed off, etc. Its suppose to make the work place safer, but in reality people are just hiding their guns.
You are on company property the second you pull into the lot. The car belongs to you but it is sitting on their property. Its kind of like having a gun in your inside pocket when you walk into a building. Its in your pocket... but your pocket is on their property. Their rules cover every square inch of the land they are paying for. The only option available would be to park your car at your dads office. A company that allows guns will get destroyed if any of their employees go on a rampage. If they say you cant have guns and an employee goes crazy their hands are clean. Its all politics....