As well as teaching players how to mark, they need to be taught how to react if they are being marked.
For a start, any of your players who are being marked in open play should treat it as a compliment. They are clearly considered to be good players who are a danger to the other team.
Advice to a player being marked
To shake off a marker in open play or at a set piece, try jogging slowly then putting in quick bursts of speed coupled with changes of direction.
If you’re being marked in open play and you can’t get away from your marker, turn the situation to your team’s advantage.
Take your marker somewhere harmless. You can even make him look really silly by taking him to your own goal line or a corner flag at the opposite end of the pitch to the action.
Even better, mark a different opposition player yourself. Now you’ve taken two of the other team’s players out of the game and created a lot of space for your team mates.
How to practise marking and getting away from a marker
Put your players into pairs. One is an attacker, the other is a defender. Tell the defenders to get to within two feet of their attacker (the ideal marking distance) and stay with him as he jogs around a playing area.
Play it like tag. Tell your attackers to try to get away from their marker and all your players to freeze when they hear your whistle.
After 30 seconds, blow the whistle. Check that the defenders are all still close to their attackers.
Switch the roles of each player.
After a couple of repetitions, you can progress by putting a goal at one end of the playing area and asking the defenders to stick close and stay “goal side” (nearer to the goal they are defending) of their attacker. This is the position they should be in when marking at corners and free kicks in and around the penalty box.
Sometimes, however, the marking player needs to be between the marked player and the ball “ball side” rather than goal side. In midfield, for example, and when running back into the penalty box with an attacker.
Progress your soccer drill by playing a small-sided game in which all players except one are allocated a player on the opposite team to mark. This is the only player they are allowed to tackle.
If a player marks or tackles the wrong player, a free kick is awarded.
The spare player on each team has a free role and can mark/tackle whoever they like.
You shouldn’t spend too much time teaching your players how to mark and what to do if they are being marked. But it’s an important part of their football “education” and it must not be neglected.