There are many ways how to defend corners. And this way I use in Football Manager 2015.
Players with top-rated attributes Marking, Anticipation, Concentration, Positioning, Jumping Reach and Strenght should be set as “Man markers”.
From this group of players, you should select players with better aerial presence and instruct those man makers to “Mark tall player”. Man makers with poorer aerial presence should have “Mark small player” instruction.
Is very useful if you instruct on the player to “Mark near post” and one to “Mark far post”. The best players for these positions are players with poorer marking ability.
If you want a player on the edge of the area to help clear the ball or start a counter-attack you should instruct of players with poorer marking ability but he can benefit from having good passing.
Another role in defending corners is a player who has better aerial presence but low marking skills. His position will be “Close down the corner”. It would be useful if you want to make it difficult for the opponent to take a short corner. It should help if you concede many goals from the near post.
What about the rest of the players?
It’s only up to you if you instruct “Zonally Mark Six Yard Box”, “Man Mark” or “Go Back”.
I use three players as “Zonally Mark Six Yard Box” and one player “Go Back” during my save for Leyton Orient in FM15.
It’s very useful to have on a player outside the penalty area in the “Stay forward” position. I use it every time. It’s up to you if it will be forward with good speed ability for counterattack or another type of player whose main goal will be to hold the ball and help the team to form.
If you play an attacking style of football and you have tall players to cover opponents, It would be useful to have two players “Stay forward”.