I would think a card swipe gate would do it. Other resort guests use their cards to get into their room. A gate would be our "room door". This wouldn't keep non-fort guests from getting on an internal bus and heading to the Meadows pool or the play grounds, but it would discourage people from just driving in.
One question though. I've only stayed at the fort 3 times, but I never felt there was a security issue. I never noticed too many people that didn't seem like they belonged there.
The settlement gets crowded with the HDD crowd, but you expect that.
j