Almost every time the opposition's winger has the ball, my CB that's closest to that side of the field will try and double-team that winger to help my FB out, leaving the space he was supposed to cover in/around the box completely unoccupied.
This also happens with CMs/CDMs trying to help my FBs too much, leaving the middle of the field at a disadvantage.
How do I stop them from doing this? I've already tried both Zonal and Man marking, I've tried asking them to close down only their own areas, and I've tried both tight marking (in the hope that they'd stick to their own man rather than chase around) and looser marking.
Nothing seems to work, double-teaming keeps occurring way too often, and my team keeps opening up unnecessary holes.
Basically, what I'm trying to accomplish is for my players to stay in their assigned positions when defending. I want my CBs on the edge of the box (or higher, depending on how high of a line I'm playing) and my CMs/CDMs in the middle of the park and dropping back just in-front of the CBs when needed. I don't want any of them drifting out to the flanks to help out my full-backs.