Sarasota Bay Watch has been working with the Reef Ball Foundation and Reef Innovations in the development of a retrofit for existing seawalls, as a step toward a living shoreline.
Below is a video explaining a project that will be hitting the water in the next month.
Video was retreived from Sarasota Baywatch https://www.youtube.com/watch?v=MOOK2GW6vsg
In many locations there is not an option to establish a living breakwater offshore and backfill to the existing seawall. This might be the best option. The project is labor intensive as modules are created then moved into place along the existing seawall.
More information is available on Eco-Rap from Reef Innovations.