The best solution to this is to build up a strong character of the child. Tell him that if he is unfairly treated or being bullied, take up the courage and feedback to the parents or teachers. Do not be shy! If you step back, the bully will move forward. A lot of the time, parents or teachers are not there to see what actually happened. Hence, he is the only one who can protect himself, so if he dare not even to tell the parents or teachers, who can help him? Build up his character, strengthen him and be his friend, so he can at least tell you what happen.