I think the problem with our defense is that we lack pace and we can get caught by quick forwards. Montero, in particular, has definitely lost a yard or two and this is worrying. Iuliano is a capable man-marker but for me he is totally brainless. Besides, I think he played really well as a left back when Pessetto got injured.
Personally, I prefer the old school left back who can keep the sideline safe than forward going right backs. That is unless you are Zanetti, Cafu, Carlos, or Contra. The main purpose of defense is not to concede goals.
Thuram has also in past played very well as a CB. He is a better man marker than Montero or Iuliano. Just look at video tapes when he played for Parma. He gives pace on the back line. Also, he is probably best tackling defender in the team beside Montero.
After all we conceded in virtually every game against quality team. Depor burned us in early moments, so did Roma, so did Lazio. Inter, Parma, Milan all managed to score against us. Just a coninicidence? I personally think that is not the case.
The best solution is to bring a good young CB but I doubt we have enough money to bring big names in January.