魔高一丈，道高一尺 [－－－－－－－－－]

Jyutping mo1 gou1 jat1 zoeng6 , dou6 gou1 jat1 cek3
Pinyin mó gāo yī zhàng , dào gāo yī chǐ

Definitions (CC-CEDICT)
  1. the devil is ten foot tall, virtue one foot (idiom); It takes constant vigilance to stave off evil.