mó gāo yī zhàng , dào gāo yī chǐ
mo2 gao1 yi1 zhang4, dao4 gao1 yi1 chi3
the devil is ten foot tall, virtue one foot
vice rises ten foot, virtue one foot
it takes constant vigilance to stave off evil
There are often variants of an idiom with just a slightly different order of phrases, but the same meaning. About this one I had the feeling that it results in a slight shift in emphasis.