When defending set-pieces would you mark a player or operate a zonal system?
The Liverpool rearguard is one of the meanest around, but their defending regularly comes under scrutiny with boss Rafael Benitez favouring defending zones rather than marking players.
It doesn't always come off though with some players confused over their duties.
Former FA technical director Howard Wilkinson and ex-Liverpool defender Alan Hansen explain why they agree with Benitez's methods.
WHAT IS ZONAL DEFENDING?
"In zonal defending, you don't mark a man, you mark an area," said Hansen, winner of seven league championships.
As you can see in the diagram above, Liverpool set up their defence for a corner with four players across the six yard box and a further four ahead of them.
Between them, they are given an area to cover and should the ball reach them, it is up to the defender to clear the danger.
Hansen added: "The three most important areas are your man on the near post, a man in the middle of the six-yard box and a man between those two."
WHY DEFEND IN ZONES AND NOT MAN-TO-MAN?
Although it tends to be more popular in European football than in Britain, Hansen is a fan of the system but admits it is down to the players involved.
He said: "We always used zonal marking when I won championships with Liverpool.
"It was all about winning the first ball and if not, you've got to clean up the second ball.
Gallas slips between the Liverpool defence to score for Chelsea
"The other thing of course was having a goalkeeper (Bruce Grobbelaar) who we knew was going to come for crosses."
Wilkinson has used the zonal system for more than 30 years in football and implemented it in many of the England teams when he was technical director at the FA.
He said: "Zonal defending is based on the principle that when free-kicks are taken in the attacking third in wide positions or from corners, there is a dangerous space which can be identified.
"Within this area roughly three out of 100 goals are scored from the first touch.
"The system attempts to concentrate the best headers of the ball in that space. Your other players are in positions to defend the second ball.
"With man-to-man marking, attackers can drag defenders all over the place by taking them away from the danger area.
"It is a collective responsibility whereas man-for-man marking is based on personal responsibility."
THE CASE STUDY
"The problem with zonal marking is that because of the movement of the opposition, you're going to have men that are unmarked," said Hansen.
"When you start off you need to decide who picks up whom and who then lets the other men go."
Sometimes players follow the ball and attackers are able to find space.
Wilkinson adds: "It's a common fault with players defending balls delivered from wide. They get attracted to a ball that they can do nothing about.
"If you can't get there, get yourself between the posts and defend the goal in case there's a second ball to deal with."
The most common opposition to the system is that zones don't score, players do, so mark the player.
But Wilkinson explains there is a further layer to the argument.
He said: "Players score from dangerous zones. What do goalkeepers do on corners anyhow?
"They zone mark because until the ball is kicked they don't know where the ball will go.
Liverpool conceded seven goals at home in the 2006/07 season
"They don't concern themselves with players, they concern themselves with the ball because it's the ball that scores."
And he dismisses the notion that defenders have to compete with attackers who have a run on them.
"Attackers get a run on you whether you are zone defending or man-for-man marking," Wilkinson said.
"They always calls the shots. You start from a standing position but once the ball is in flight, you've got the distance the ball travels to get yourself moving.
"Lots of teams in the Premiership mark zones on the wide free-kick, because if you try and mark runners you end up running into each other and you can't jump anyway.
"You've got to remember that the higher up you go, the greater the quality of the delivery.
"That's one thing you can't do anything about, you have to assume that the people who are taking it can hit the button."
TEACHING THE SYSTEM
Liverpool's defending as a team has been widely praised with the team matching a club record for consecutive clean sheets in the league.
Wilkinson says: "Benitez's record, before he came to Liverpool and since he arrived, says that undoubtedly in achieving some things he's a master.
"I'd be careful about arguing with him on defending because his record isn't bad, particularly in Europe.
"It is a difficult thing to coach. It's more complex than man-to-man but it is more effective.
"But it's only more effective if it's covered comprehensively and players understand not only their roles but the roles of others."