[MrJohnston]

I look at the secret passage like this:
It's the human player feeder station. It's perfectly reasonable to make the feeder station a "protected area." The difference in this game is that game pieces being sent through are more attainable by the opposition than before.

Consider:
* The human player is required to send boulders out at a certain point - whether that alliance's robot is ready or not.
* All boulders sent through the station will spent some time on the ground - and likely not in the possession of the intended bot.

In other words, we have a feeder station that is inviting the opposition to swipe the game pieces.... They just have to be really, really careful.

I can see a real value in a new type of defense at high levels: An offensive bot that specializes in quickly grabbing boulders in the opponents' secret passage.... And I can see human players rolling a tantalizing boulder out just a wee before their robot arrives, tempting said bot to make an error in judgment.... There could be some interesting play around this....