YOU SAID:

who has eyes on the back of their head.

INTO JAPANESE

後頭部に目をつけている。

BACK INTO ENGLISH

I have my eyes on the back of my head.

INTO JAPANESE

後頭部に目がある。

BACK INTO ENGLISH

There is an eye in the back of the head.

INTO JAPANESE

後頭部に眼がある。

BACK INTO ENGLISH

There is an eye in the back of the head.