When a dream places something behind you, it is symbolically putting it in the past. This is in much the same way you would encourage someone to deal with a traumatic event and ask them to put it behind them. In other words do not keep looking at it day after day.
If someone is chasing you, it means something from the past still has a power over you today. While you may feel you are past it, the dreams shows that you are still expending energy trying to get distance between you and it. The feeling that comes up in dreams like this is the key. The dream is attempting to show you that there is a link between the past trauma and that feeling today. If it is a parent, it means that you still have issues with that parent today.