Custom Scenario... PLEASE HELP!

Hi r/aoe3,

I've been playing AOE2 for years and FINALLY got AOE3. (Really, really, really, REALLY late to the party, I know)

I'm having an issue with a custom scenario I'm trying to work on and it COULD be an easy, noobie mistake fix. Or it could be something else. I don't know.

BASICALLY, I have a fortress. There are units in the fortress at certain positions and I DO NOT WANT THEM TO MOVE WHEN THE SCENARIO STARTS. And yet I have found no way to adjust their behavior to NEUTRAL aside from in-game options, which by that point is too late because they've already started moving.

Please tell me what I need to do to fix this. It is driving me CRAZY...

Thanks!