The figures seem to be taken from the work of building up and pulling down houses. In their general application, they recommend the man who would act wisely to be cautious when taking any step in life which involves risk.
Breaketh an hedge - Rather: “breaks through a wall.”
Serpent - The habit of snakes is to nestle in a chink of a wall, or among stones (compare Amos 5:19).
Be endangered - Rather: “cut himself.”