Prophylaxis

Walter de Chepe's Prophylaxis "protects a person, city or object from magic spells", however it frequently takes a much stronger effect than desired, so much so that "objects become impervious to human or fairy agency of any sort whether magical or not." In 1280, the spell was cast on the town of Bristol with the intent of protecting the community from spells, but was so powerful that nothing and no-one within the town's boundaries was able to move at all until the Raven King came south in person to remedy matters [50]. Prophylaxis - the word generally means the prevention of disease - is apparently based on a piece of fairy magic.
See also Prophylactics against magic