Djourou/Kos/Squillaci are a joke, as are Sagna/Gibbs, but a HUGE amount of why they suck is complete lack of discipline, they refuse to stay in line, our fullbacks are consistantly getting caught upfield.
Ashley cole will bomb upfield then bomb back, even when not being attacked. You get back in position and set yourself so you're READY for any attacks. Sagna and even more so now Gibbs bomb up field, walk back, and if theres an attack they run after the player rather than being in position and have that playing coming at them, makes the world of difference because then our CB's are rushing out to do the fullbacks work, and then our CB's are out of position. The amount of times a team would just send a long ball into the left/right back area with a striker running on to it, with Kos or Djourou rushing out and making a daft tackle with fullbacks not in sight was ridiculous.
THeres zero discipline in our defence, whoever is training/organising it is a joke. At the very least with Verm/Gallas/Toure in any pair you had two incredibly good CB's who made up for Sagna's mistakes, with just one of those three, and another completely crap CB our positioning is a joke. Defensively its funny, we got away with a huge number of mistakes, in so much as it not costing us goals, Djourou got away with so many bad tackles and put in a lot of great last ditch tackles he shouldn't have needed to make.
But our offence should take the blame also, in 12 of the 17 games after the 1st leg against Barca we scored 1 goal or less, Arsenal haven't been "1 nil to the Arsenal" for ridiculously long, we've been "we'll score one more than you" type Arsenal. Our offence was entirely as much to blame as the defence,