How had Mr. Radley seen to it that his younger son Arthur (Boo) caused "no further trouble" in Maycomb in To Kill a Mockingbird?
Arthur Radley Jr. was arrested as a teenager, along with several of the Cunninghams from Old Sarum, and
... came before the probate judge on charges of disorderly conduct, disturbing the peace, assault and battery, and using abusive and profane language in the presence and hearing of a female.
While the other boys were sentenced to the state industrial school "and received the best secondary education to be had in the state," Arthur's father decided that it was a "disgrace," and that his son was undeserving of such a place. So, Mr. Radley promised the judge that there would be no more trouble from his son if Arthur Jr. was released into his custody. Mr. Radley's punishment apparently consisted of confining Boo within the walls of the Radley House, and
... Mr. Radley's boy was not seen again for fifteen years.
When Boo got into trouble again for stabbing his father in the leg with a pair of scissors, Mr. Radley again saw to it that Boo was not charged, and Boo again returned to his confinement in the Radley House, and no one besides his family--and possibly Dr. Reynolds--had seen Boo since.