That might be okay. Sand can be sifted and gravel and cigarette butts separate by density with shaking the container. Sand and pebbles can then be returned to

That might be okay. Sand can be sifted and gravel and cigarette butts separate by density with shaking the container. Sand and pebbles can then be returned to beach. (Sand depletion is a concern in many areas.). Robo-dog could return to a dock which automates part of that separation process. Then return the sand to the same spot. Cleaning might be a concern (spreading spores of invasive species) if used in different areas.