Erosion happens. It's natural and it's expected. Add rising sea levels (from whatever cause) and you have... more erosion. Our coastal borders have never been permanent, they are always shifting.
So how can we deal with beach and wave preservation? We do the opposite of building concrete sea walls (which simply accelerate erosion). We let the borders naturally grow and shrink.
How should we deal with shifting coastlines? Here is the best answer I've seen.