rod for one's back

idiomatic

(idiomatic) The means of one's own punishment or downfall.

Japanese Meaning

自ら招いた罰や破滅の手段 / 自業自得の懲罰、すなわち自分自身にかかる罰 / 自分自身が原因で招く災い・破滅の手段

Careless bookkeeping can turn into a rod for one's back when audits begin.

ずさんな帳簿管理は、監査が始まると自らの破滅の原因になりかねない。

Sense（1）

(idiomatic) The means of one's own punishment or downfall.