Optionally, membranes may comprise molded or extruded layers of rubbery material with or without fiber reinforcement within or between the layers, for example woven or non-woven material, e.g., cloth or netting, containing natural and/or synthetic fiber, such as cotton, polyester, polypropylene, glass or Kevlar (???) fiber. [0191] Surface features may be provided on the membranes to assist in secu