defend, prevent

防 is composed of the radical 阜 (mound) and 方 (square). 阜 is a pictograph of a hillside; mountains act as natural barriers that shield against wind and rain. 方 is a pictograph of a criminal bound in wooden shackles and exiled to a distant place, implying a border region. Because borders require vigilance and defense, 防 came to represent guarding against or defending.