おに金棒 かなぼう
onini kanabō

Idiomatic Expression

1. making something strong even stronger; solidifying something's chances; (giving) a metal rod to an ogre — literal

きみ英語 えうごができれば おに金棒 かなぼうなんだが。
kimiga ēgoga dekireba onini kanabōna ndaga.
If you could only speak English, you would be perfect.