The Swashbuckler's 1st-level deed Opportune Parry and Riposte states:
Opportune Parry and Riposte (Ex): At 1st level, when an opponent makes a melee attack against the swashbuckler, she can spend 1 panache point and expend a use of an attack of opportunity to attempt to parry that attack.
The description of the line in the sand spell states:
You create a glowing crimson line around the area. Against creatures in the area, you can attempt a number of additional attacks of opportunity per round equal to your spellcasting ability score modifier (Intelligence for magi and wizards, Charisma for bloodragers and sorcerers), although this does not allow you to make more than one attack against a creature per action that provokes.
Can you make multiple parry-ripostes in the area of the spell?