The roller is just a big stone. Due to long-term use, it must be tainted with a trace of spirituality. It's like consecration, which is to infuse the human spirit into an object. Stones belong to mountains. It cannot be placed directly opposite the door. Because the door is for collecting wealth, and wealth belongs to water. If you block the water, you will definitely lose money. This is a bit like the role of Shi Gandang. Generally there is space behind the house. When the crowd is slow, just after the back of the house is consecrated. Choose a good day and it will work. It is equivalent to the role of a backer. Of course, what I said is not absolute. In some cases, it can also be installed in front of the door. But that's too complicated to say. In short, the basic principle is still the same. There are many artifacts in Feng Shui. Generally speaking, one must be spiritual and enlightened. As long as the key points are identified and laid out, they will be the finishing touch.