>Yeah, right. And I'm not going to notice a unit that I didn't build, and that I can't control, moving around my empire without me telling it to? Maybe the AI is that dumb, but I doubt many human players are.<
I was aware of the problem. But, an extra slinger/archer that listens to you most of time but moves at its will one out of say 5 times may not be that easy to catch. What if that little spy slinger always listens to you?! You probably will never notice, unless you keep an account of all units you produce every turn you play. In a big map where lots of units have to be managed, you may not be able to do so. Maybe you only have to keep an eye on those at the country border and make sure you don't have a too uniform mix of units. Else, an extra slinger will not necessarilt tell you which slinger is the spy. Of course, the spy has to be able to receive your command and decide whether or not he wants to obey.
>but what's the fun in that? A little memory, say allowing n turns to continue "seeing" a unit in the fog (but not any movement or changes), should not be hard to implement and certainly easier then a look-ahead predictive strategy.<
Even that is not too helpful to AI. A cheaper way (in terms of memeory consumption) can be to set a bit flag for each hex the AI just visited and the flag is on for N turns. All hexes flagged are deemed visible. Although AI can see your unit movement for a while, it knows that only for N turns. A human player can remember and can predict what you would do later. The AI is not too good at that and thus is allowed to see your movement for N turns.
In any case, I still like the idea of having a spy system, but I haven't figured out a scheme for it work seamlessly with the current setup.
Bright was the moon and deep the night;
The stars twinkled, of great delight.
With wings of dream, I searched my soul
To know its truth and find my role.
By French Kisser, a chaser after and believer in true and ingenuous romance.