[Behind the building] is too general! First of all, the more important thing is: does the entrance of the residential building where you live, the so-called main entrance in Feng Shui, face the traffic police team? If the entrance door is facing the traffic police team, it will be a serious offense! Bad luck! ----You can use cement to build a thin snake-shaped bend in front of the door of the residential building, slightly longer than the width of the door opening, to block evil spirits. In addition, above the doorway, write a talisman in red paint, which can be dissolved.
If the door is not facing the traffic police, but the back of the residential building is facing. You can put an octagonal mirror on the lintel frame of the balcony window of your home that faces the traffic police team. Reflect and eliminate evil spirits.