The War of the Roses

Lawyer Gavin D'Amato is in his office discussing a divorce case with a client. Noticing the man's determination to divorce his wife, Gavin decides to tell him the story of one of his clients, a personal friend of his.
Oliver Rose, a student at Harvard Law School, meets Barbara at an auction, where they bid on the same antique. Oliver chats Barbara up and they become friends. When Barbara misses her ferry home, the two end up spending the night together at a local hotel. Eventually the two marry and have two children, Josh and Carolyn. Over the years, the Roses grow richer, and Barbara finds an old mansion whose owner has recently died, purchases it and devotes her time to making a home there. However, cracks seem to be forming in the family. As Oliver becomes a successful partner in his law firm, Barbara, who was a doting and loving wife early in the marriage, appears to grow restless in her life with Oliver, and begins to dislike him immensely.
Oliver, for his part, cannot understand what he has done to earn Barbara's contempt, despite his controlling, self-centered, and generally dismissive behavior toward her. When Oliver believes he is suffering a heart attack, (actually a hiatal hernia) the day after an argument, Barbara (after her initial shock and concern) realizes she felt a sense of relief that he might be dead. She tells him so, adding that she no longer loves him and wants a divorce and Oliver accepts. Feeling that it might not be wise to represent himself, Oliver hires Gavin as his legal counsel on a retainer.
Tension arises between Oliver and Barbara during negotiations when it becomes clear that she wants the house and everything in it. When Barbara's lawyer uses Oliver's final love note to her (which he had written in the hospital) as leverage against him in their legal battle, she refuses to back down. Barbara initially throws Oliver out of the house, but he moves back in after discovering a loophole in the divorce that allows him to stay. As a result, Barbara immediately begins plotting to remove Oliver herself, even trying to seduce Oliver's lawyer Gavin into siding with her instead.
In an effort to win the house, Oliver offers his wife a considerable sum of cash in exchange for the house, but Barbara still refuses to settle. Realizing that his client is in a no-win situation, Gavin advises Oliver to cave into all of Barbara's demands, leave her everything and start a new life for himself. In return, Oliver fires Gavin and takes matters into his own hands. At this point, Oliver and Barbara begin spiting and humiliating each other in every way possible, even in front of friends and potential business clients. Both begin destroying the house furnishings; the stove, furniture, Staffordshire ornaments, and plates. Another fight results in a battle where Barbara nearly kills Oliver by using her monster truck to run over Oliver's prized sports car, a classic Morgan 4/4. In addition, Oliver accidentally runs over Barbara's cat in the driveway with his car. When Barbara finds out, she retaliates by trapping him inside his in-house sauna, where he nearly succumbs to heatstroke and dehydration.
While the kids are away at college, Oliver eventually calms down and attempts to make peace with Barbara over an elegant dinner, but reaches his breaking point when Barbara serves him a pÃ¢tÃ© which she implies was made from his dog (the dog is later seen to actually be alive and well outside). Oliver attacks Barbara, who flees into the attic. Oliver boards up the house to prevent Barbara from escaping, while Barbara loosens the chandelier to drop on Oliver in yet another attempt to kill him. When their live-in housekeeper Susan returns home in the middle of the climactic battle, she senses something is terribly wrong and discreetly contacts Gavin for help. By the time Gavin arrives, Oliver and Barbara's quarrel has culminated in the two hanging dangerously from the unsecured chandelier. During this time, Oliver admits to Barbara that despite their hardships, he always loved her, but Barbara does not respond. Before Gavin can come inside with a ladder, the combined weight of Barbara, Oliver and the chandelier is too much for the electrical wires, which snap and sends them crashing violently to the floor. In his final breaths, Oliver reaches out to touch Barbara's shoulder, but Barbara uses her last ounce of strength to knock his hand away, firmly asserting her feelings for him even in death.
Finishing his story, Gavin presents his client with two options: either proceed with the divorce and risk facing a horrific bloodbath in court, or go home to his wife to settle their differences properly. The client chooses the latter, and Gavin, satisfied, calls his wife to tell her he is on his way home and that he loves her.

Question: Oliver boards up the house to keep who from escaping?
Answer: Barbara