Once a few rocks are in scoring position, they can be protected with guard stones. A guard is a rock that stops in front of the house to make it tougher for an opponent to knock out stone in the house. Guards are part of the aggressive style of curling. With more stones in play, shots become more difficult. Players trying to thread a stone through a cluttered area will sometimes bump into an opposing stone, ruining the intended shot.
Aggressive play opens the door for teams to score several points in a single end.
At the start of an offensive end, a team can choose to take advantage of the Free Guard Zone. If the first four stones of an end come to rest in front of the house, they cannot be immediately bumped out of play. Later stones can bump those stones out of play. With all the factors that come into play for a single shot, experience becomes a valuable commodity. Chances are good that veteran curlers have encountered most situations at one time or another.