Netting constructed from strong elongated tubular elements encloses optic fiber signal lines. Such netting is anchored at spaced locations underwater adjacent to a dock to establish a protection zone for sea vessels within the zone from terrorist threats to be delivered underwater by penetration or attempted penetration of the netting which may also block damaging impact inflicted on sea vessels within the zone by missiles. If a missile however penetrates the netting for impacting the sea vessel, the location of such netting penetration is then indicated through the signal lines so as to enable rapid threat response.