Put as many people (14 years old and up) as you can on repairing the wall. Keep putting them on until the job is done. (Yes, they can and will wander off.) To put several people on repairing the wall, grab a person, and hover over the bucket by the wall until you see "[Person] sees the bucket.", then drop them. Repeat the process, checking each time to make sure they are actually repairing the wall. Good luck!