I have had a similar discussion with many engineers. Knowing that they technically should have their asic displayed on their chest visable, but was kindly corrected with the H&S issues of having an item hanging loosely around their neck while working on an engine.
As for access to your property i tend to belieave that you are right, they should not be just walking in. Noone has that right, they have to report to the office and then be granted access into your hangar.