How to deal with enemy spies?

[ooji]

I could easily counter enemy assassins with my own assassins. However, I don't know what to do with their spies. Once enemy spies get certain subterfuge skills, it becomes nearly impossible to assassinate them and they can't be bribed either. They cause unrest in my cities, sometimes as much as 80% unrest. Anyone know how to deal with them?

[athanaric]

I could easily counter enemy assassins with my own assassins. However, I don't know what to do with their spies. Once enemy spies get certain subterfuge skills, it becomes nearly impossible to assassinate them and they can't be bribed either. They cause unrest in my cities, sometimes as much as 80% unrest. Anyone know how to deal with them?

Put spies of your own in any city that's been infested with an enemy spy. In fact, put a spy in any city whose province has a border with an AI faction. If the enemy succeeds in infiltrating your city anyway, move another spy in there. It helps if your own spies have high skill levels. If two spies can't get rid of the infiltrator, use more. Also, there are always some governors with traits (suspicious, xenophobic, etc.) that make discovering spies easier.
As for assassins, train them on enemy assassins and on diplomats. Once they've reached a certain level, they should be able to kill low-level enemy spies, too.

Spies can be bribed if they're with an army or in a city of their own faction.

[Boriak]

Recruit your own spies, then send them spying after enemy (or even neutral and allied) armies. First spy after armies with no commanders as the odds of getting captured raise dramatically if there's a general present. You will lose some spies but that's the way of the spying business. After one or two successful espionage attempts, your spy should receive extra traits and ancillaries (prostitutes and such). Send them spying after diplomats and generals (carefully!) after that so that their skills really improve. When they gain 5+ eyes, you can start sending them against armies with strong generals and cities to open doors or just cause havoc in an enemy's city, possibly making that city revolt (I love doing that with enemy superpowers, occupies them and that gives me a respite if I'm hard pressed).

Leaving a spy in a city as a counter-spy (or as I like to call them nowadays, a varys ) can be beneficial but I tend to send mine in the field. I will keep a spy or two close by so they can sweep a city that suddenly developed a drop in happiness - chances are an enemy spy infiltrated it.

I could mention that I hardly ever build watch towers. Instead, I send a not-too-bright spy to patrol an area. In the past, I've had two spies patrol Iberia though that could be done with a single one. I used two for the entirety of Egypt - one patrols the northern part, the second from Memphis and south. It's easy to plot a multi-turn path for a spy and then he walks it by himself until reaching the end. Saves me money I would spend on towers.