Help With A Defense Issue

[kocaelispor]

I am sorry to open a lot of threads but I enjoy to ask you some advices.

I manager Stuttgart.

Altoughy my midfield and strikers are doing good in attacking and creating positions;

I have some issues with my defenders as;

1) low tackle completion

2) they always stays behind the opponent strikers.

I have 2 cbs; Khaled Boulahrouz and Serdar Tasci with man marking. They also possess a great pace.

My full backs are Molinaro and Celozzi and they are good players.

Should I change mentality, marking, tackling, closing down settings?

Please help mates.