Concrete Tetrapods are a proven established solution used world-wide for coastal erosion.
The Tetrapod shape is designed to dissipate the force of incoming waves by filtering the energy and allowing water to flow around, rather than against it. Stability is dictated by self-weight and interlocking with surrounding units making them difficult to dislodge.
Earlier barrier material used in breakwaters, such as boulders and conventional blocks, tended to become dislodged over time by the force of the ocean constantly crashing against them. Tetrapods are designed to remain stable under even the most extreme weather and marine conditions, and when arranged together they create an interlocking porous barrier that disbands the power of waves and currents, stopping any backwash.