He needs recall training as Knute suggested. You can make it a game to call him to you, reward, then have your brother call the dog to him, reward, etc., etc. back and forth. Start off fairly close together and slowly increase the distance and start adding distractions. Don't go too fast. Make sure his recall is solid before moving on to the next step.
Practice this every time you take him out. Have him on a long lead and when he gets half way, call him back and reward. Then start doing it when he gets almost to the end. Call him back and reward. Eventually (we're talking months) you will be able to have him off leash and he will either stay close on his own, or at least come back when called. Even at that point, practice randomly calling him back to you and reward.
Practice this every time you take him out. Have him on a long lead and when he gets half way, call him back and reward. Then start doing it when he gets almost to the end. Call him back and reward. Eventually (we're talking months) you will be able to have him off leash and he will either stay close on his own, or at least come back when called. Even at that point, practice randomly calling him back to you and reward.
