We are starting to deploy buoys to demarcate no entry, no-take zones in a recently declared Marine Fisheries Management Area in Cambodia, and would like advice on materials and design for the marker buoy attachment and anchoring system.

We have 1 m diameter and  0.6 m high cyclindrical concrete blocks filled with metal, which we plan to attach to rope and chain, within minimum 3 m of chain near the surface to prevent the buoys being stolen.  The buoys are officially marker buoys (not mooring buoys) but inevitably there will be some unwitting boats that moor to the buoys.  Planned locations and proposed design attached.

Specific Questions:

• CHAIN & SHACKLES: Is stainless steel the best material for chains and shackles?  Stainless steel chains (low grade e.g. 201), galvanized steel chains and also galvanized steel cable are available in the shops here.
• ROPE: Is nylon the best material for rope? What thickness would be necessary?
• DESIGN: Do we need chain at the bottom or will rope be enough?  I.e. Concrete block - Chain - Rope - Chain - Buoy, or Concrete block -  rope -  chain - buoy?

Any advice from engineers (or those with experience or knowledge of construction in marine areas) would be most appreciated, thanks!