I don't think it's the individual players that are the problem, we just don't seem to be defending as a unit the way we used to. It could be because players are getting dragged out of position to easily or it could be that because the full backs are getting forward more it is leaving gaps, but there just doesn't seem to be a blue brick wall at the back.
I would like to see Fellaini being put back into centre midfield for a while as he does a great holding job and provides such good cover for the defence. Obviously he is also doing a great job up front, but teams are setting up defensively with him in mind, so it would also have the added benefit of buggering up their plans.
While Naismith isn't the greatest player, he did have a really good partnership with Jelavic at Rangers, so woul dlike to see that combination tried out for us.