Balustrade, Bank, Bar, Barrage, Barricade, Bastion, Battlement, Block, Blockade, Blockage, Bolt, Boom, Bottleneck, Boundary, Breakwater, Buffer, Bulkhead, Bulwark, Bumper, Choking, Clog, Cofferdam, Congestion, Constipation, Curtain, Cushion, Dam, Diaphragm, Ditch, Division, Drawbridge, Earthwork, Embankment, Embolism, Enclosure, Entanglement, Escarp, Escarpment, Fence, Fender, Fieldwork, Fortification, Frontier, Gate, Gorge, Groin, Hindrance, Impasse, Impediment, Infarct, Infarction, Jam, Jetty, Limit, Lock, Logjam, Loophole, Mat, Midriff, Moat, Mole, Mound, Obstacle, Obstruction, Outwork, Pad, Padlock, Palisade, Panel, Parapet, Partition, Portcullis, Rail, Railing, Rampart, Redoubt, Roadblock, Scarp, Separation, Stockade, Stop, Stoppage, Strangulation, Wall, Weir, Work