Ishibashi o tataite wataru (石橋を叩いて渡る): to tap on a stone bridge before crossing it. Even a bridge that looks solid is checked for safety first. Doing things with caution on top of caution.
Sonae areba urei nashi (備えあれば憂いなし): if prepared, no worries. A person who is always ready for an emergency need not worry when one happens.
Nen ni wa nen o ireyo (念には念を入れよ): add care to care. In important matters, take great care that no mistake happens, and then check once more.