The phrase "be prone" implies being susceptible or likely to experience something negative, such as illness or injury. Its antonyms include "be resistant," "be immune," and "be impervious," which suggest having a strong defense mechanism against the negative occurrence. "Be invulnerable" and "be insusceptible" also denote the ability to withstand harm or danger. Conversely, "be inclined" or "be disposed" are synonyms for "be prone," indicating a tendency or natural inclination towards something positive. Selecting the appropriate antonym for "be prone" depends on the context and desired connotation.