Hi Hannibal,
If you're talking about one single unit, then I advise you to use an AI, were that soldier can't move any longer. (However, it will attack you when you get near it) I used the 'Immobile Units' AI from Zanzard Lothar in the Blacksmith. That works fine.
If you're talking about several units, then you'll have to freeze them, I don't know why it doesn't work with you. One thing I know for sure, you can't unfreeze units! (When you freeze them, they stay in that position the rest of the game!)
By the way, did anyone tried to freeze a monk? It doesn't seems to work? Thnx (lcoffyn@yahoo.com)