Eto'o is my favorite striker. But Matthecat has converted me and I have decided to play with Italy as my team of choice. I always win against Barca and Man Utd, because most kids just try to pass the ball to the runners (Eto'o, Messi, Rooney, Ronaldo) and I just stop them. MatTheCat, you are right it is fun to make those kids upset.
Anyway, to defend against Eto'o you must man mark with a physical, fast midfielder (probably DMF). Don't mark him aggressively, because he will follow him around insistently and leave gaps in the defense. I usually don’t use AI pressure, because it will leave gaps as well. What I do is just quickly switch players with L1 (I use the semi-assisted cursor) and I never sprint. I just place cannavaro in front of him at it works.
Also, I use a tree formation (5-3-1-1) for defending tactics (Strategy A) and just use it every time the opposition has the ball. Make sure that you fix the manual marking settings on this formation as well.