As in, "The best Defense is a strong Offense." To me, Espionage is hopelessly weighted in favor of the attacker. You only have a small number of spies available to you. Defensively, you have to guard ALL of your cities, each of which could have as many as ten targets that need to be defended. You could easily use up your entire allotment of spies guarding just ONE city. Which means that the rest of the nation is wide open to infiltration from enemy spies. It's ridiculous to have so few spies in nations that will grow to populations in excess of millions of citizens. What is currently a representation of individual spies should actually fully fleshed out espionage networks. And just like the FBI maintains field offices in EVERY major city, they should be monitoring Security issues in every sector of the city and the surrounding area. Of course, absolutely thorough coverage gets EXPENSIVE, and most FBI field offices complain they are understaffed. "He who tries to protect EVERYTHING usually ends up protecting NOTHING." I suggest that it be left to the player just how much he wants to invest in Security the same way he decides to handle National Security. That is, the making and deploying of ANY NUMBER of units. (In this case, Spies.) Make it that, say, an allocation of 10 Spies would make a city's Security airtight. Less than that gives an enemy agent a percentage probability of getting past that Security.