A trigger_teleport with 1/3 effectiveness?

Generic question:
How would you make something that allows a user to only activate one out of three trigger_teleports?

Specific application with my map project:
I have a Star Trek ship like the Enterprise. In the same map there is a shuttlecraft outside the Enterprise. I have it where you can teleport (transport) from the Enterprise to the shuttle (and get health/battery) and back. But to balance that benefit I want to have it where someone on the Enterprise can detect that a person is on the shuttle, and the person on the Enterprise can then try to "get a transporter lock" and beam the shuttle occupant off the shuttle, strip their weapons, and put them in the brig. But in keeping with the Star Trek theme, I want this transport to be less than 100% efficient, in that the person on the Enterprise might not "get a lock". In short, I want them to be able to succeed say only 33% of the time. So, I was going down this path ...
a) Have 3 geographic zones in the shuttle.
b) Have a separate trigger_teleport that covers each zone.
c) Have it so the person on the Enterprise can only activate one of the three trigger_teleports. If he is lucky, the shutttle occupant is in the correct/corresponding zone. This will happen about 33% of the time.
d) Put a delay before reset on the teleport so that by the time the person on the Enterprise tries again, the shuttle could be unoccupied.
e) To detect shuttle occupancy, I was going to have a trigger that covers the entire shuttle that can be tied to something on the Enterprise to say "someone is on the shuttle, but you don't know which zone."

I know it's wordy. Sorry.

Its been way to long for me but my suggestion is simple. Find you a quality prefab site. Download something similar to your want and either use it (with a corresponding thank you to the author) or edit it as strongly as necessary and use it (also with a thanx to the original author)

Prefabs are the single most under used, and/or thankless items in Half-Life editing.

You can learn so much more from prefabs, than trying from scratch. Its less rewarding for your self interest, but you can always make it up in the future by helping others once you become the guru.

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The best things in life, aren't things.