A friend was telling me about a memorial in which Jochen Gerz had some involvement. It was to mark the loss of the countless synagogues destroyed in Germany during the second world war. There was a secret component to this work in that the names of the synagogues were marked on the underside of paving stones which were then used to replace existing paving stones. Only the people immediately involved in the project know the whereabouts of these stones. I don't know if they are free to pass along these locations, but, at any rate, I think it is a very successful instance of memorialization because it is constructed in the living memories of the people involved as well as having a physical manifestation. In a metonymic way it reproduces a loss, or disappearance, that is co-extensive with the greater loss of the synagogues.
With the monument I am planning, an indication of that which has been lost will have the opportunity to make itself known through periodic but rare appearances in shadow form (a mere shadow of a representation).