I would be leery of concrete blocks at the foot of a beach, they can be a bugger to step on or almost step on or slide off of with bare feet, with a good chance of leaving a little skin on the edges, I can almost feel it just thinking about it. if you could make a little berm out of some larger river rock or even 3" limestone would be way more forgiving I would think then blocks. seems like anything 2 to 3" diameter should not erode away if it is several ft under water. jmo

All the really good ideas I've ever had came to me while I was milking a cow.