Revetments, armories, groins, jetties, ripraps — the walls of stone built to protect a length of bluff from erosion go by many names, but in whatever guise they pose a growing threat to the Vineyard shoreline, according to several prominent Island environmentalists. A modern Vineyard revetment constitutes tons of boulders, often freighted to the Island by barge and fitted, puzzle-like into the bluff over geofabric layering to absorb the force of storm impact. Despite the large associated costs, it’s a security that more homeowners are likely to seek in an era of global climate change, says Vineyard conservation society chairman Brendan O’Neill.