Shadows are allowed outside the yard, but most people don't. In ancient times, if civilians built a screen wall outside the courtyard, or government officials did not build it according to the standard, they would be beheaded. The building standards of ministers are strictly regulated and the grades are very strict.
I wonder why you want to build a screen wall outside the courtyard. Most people nowadays don't believe in evil and can do whatever they want. Didn't someone leave mascots like lions and unicorns around? So whether you can put it down or not, dare not assert it, please consider it carefully, or ask the Feng Shui master to make a decision.