THis seems pretty murky to me. I can't seem to espionage anything because my spy is discovered as soon as I get to the target city. How do I prevent the spy from being detected. In addition I keep finding spies in my territory but I don't know how I do it. My spy doesn't seem to see them (although I don't know how this works since the global line of sight should be different than the spy's line of sight.

So how do I increase the odds that I find spies and how do I decrease the odds that my spy is caught?