How do I mask game objects outside of volumetric area

I am creating an AR infinite runner in which objects are instantiated at one end of the playable area and move towards the opposite end of the playable area to ultimately disappear once it moves outside of the playable area.

The issue that I am having is that I want the game object to be masked out once it moves outside the area. Since I am using AR in which the player can position the camera however they prefer, I can't find an easy way to do it with a depth mask shader since it will hide objects prematurely if I move the camera to the wrong position. Is there a way to simply mask objects that move outside of a volumetric area?