CSU Extension Slugs often avoid travelling over materials that are high in acid, alkaline or are abrasive. Diatomaceous earth, wood ashes and similar materials placed around plants provide some protection. However, the effect of these treatments is reduced by exposure to moisture.
Salt also is toxic to slugs and direct applications of table salt to a slug can kill it.
This technique has limited usefulness since excessive salt in a garden can affect plants. Certain metal ions also are highly repellent to slugs. Barriers of copper foil exclude slugs from greenhouse benches and raised bed plantings. Other copper-based materials, such as copper sulfate, repel slugs.