From: Rabbi Moshe Sofer
To: Unknown recipient
A community places the upright poles of a tzuras ha-pesach inside a courtyard behind a wall, since authorities prohibit structures in the public domain. The Chasam Sofer rules this valid, since tzuras ha-pesach functions as a mechitzah and does not require visibility, but recommends attaching a small outer pole as an extra precaution.
Source: Shu"t Chasam Sofer OC §96