There is an open space behind the house. How to resolve this bad feng shui?

The main problem from your description is that there is no backing, the foundation is unstable, and the population is disadvantaged.

You can place a large round stone or rockery stone at the center of the wall of your house on the mountain side (i.e., the lying position) to create an artificial backing to protect your family's health.

Because the back you are talking about may be the back of the building. The direction of your home should be determined by the direction of your own door, not the entire building, so the back may not be the back of your house. Location. You only live in one unit in the building and don't have to look at the layout of the entire building.

If you can see open space from the window, you can place green plants on the windowsill to block it, because this depends on the environment and form. It does not mean that open space is not good. It mainly depends on whether there is a bad shape and the seating area. Upward with or without defects.

It is convenient to provide pictures and the correct sitting direction, otherwise it will be easy to talk in vain.

Hope it helps.