need defensive tips with my 4-2-3-1 arsenal tactic

Hello all

I have recently entered my 3rd season with my beloved Arsenal. Progress has been steady. Season 1 I scraped 4th (surprise surprise!!).

I decided to move my two CM's (wilshere and ramsey) down to DM's playing as a regista and DM respectively.

It certainly helped, we lost the title to Chelski by a point on the last day of the season so definitely progress.

In the summer I decided to heavily invest in beefing up my defense as I felt we lost the title in the first 3 months of the season by conceding too many goals.

You can see in the screenshots my new additions and the roles they play within the squad. They are all solid players but I can't understand why I can't keep any clean sheets.
Please take a look through the tactic and advise where I am going wrong. I'm at my wits end with this. I know I have a squad capable of dominating both domestically and in Europe.

Thanks in advance.

http://www.mediafire.com/view/76fhppkfrdaa3ef/231670_2015-01-12_00009.png

http://www.mediafire.com/view/lbbi414rgm84alw/231670_2015-01-12_00010.png

http://www.mediafire.com/view/ql7v7aszmpdj021/231670_2015-01-12_00007.png

http://www.mediafire.com/view/514f4g40b7h8i70/231670_2015-01-12_00006.png

http://www.mediafire.com/view/n25eevk97776mei/231670_2015-01-12_00008.png