Perowne Barracks [1963- ]
The place mark is an approximation of the entrance, based on the Wiki entry, saying Perowne Barracks was on the other side of Castle Peak Road, opposite Gordon Hard. It's present day location is occupied by the Immigration Training Acadamy as well as the construction site of the Chu Hai Collage, a football field up in the hill, and some re-developments there.
From Street View you should be able to see the old entrance but that's it. Google Earth seem to be still showing some older buildings an the Immigration Acadamy.
The wiki entry also mentioned the Tuen Mun Highway bisected the compound. The site was pretty big. Part of it is now being used by the Crossroads International. It would seem Crossroads had kept one of the guard post at their end of the entrance for their own use, as seen from Street View. Some old wire fance, and some old buildings seemed to be intact. Look it up on a Map and you should see how far it goes.
We need an old map to find out its previous boundary.