Let's put is in simple terms...Physical barriers, Detection, Assesment, and last but not least, Response. This should cost you roughly a buttload(read Tens of Millions of Dollars or a company sized element for full time protection)of cash. Without going into details, I have a bit of experience in this realm and the bad guy always had the advantage of suprise and foreknowledge. Best bet is to withdraw, consolidate and defend from a smaller more reinforceable location.
Dead or alive, my guns are coming with me