A Denton man has pleaded guilty to trying to sell his daughter as a sex slave. Steven Marks was sentenced to four years in prison. Marks, his father, and his mother were arrested in Rockwall after the 14-year-old girl escaped and called for help. Marks was accused of driving the girl to the Chicago area and selling her for just over $15,000. But the buyer could only come up with half the money, so Marks took her back.