YOU SAID:

I've spied on him for 5 hours and I don't see him do anything.

INTO JAPANESE

私は5時間彼を監視しましたが、彼が何もしているのを見たことがありません。

BACK INTO ENGLISH

I watched him for 5 hours and never saw him do anything.

INTO JAPANESE

私は5時間彼を観察しましたが、彼が何もするのを一度も見ませんでした。

BACK INTO ENGLISH

I watched him for five hours and never saw him do anything.

INTO JAPANESE

私は5時間彼を観察したが、彼が何もするのを見たことはなかった。

BACK INTO ENGLISH

I watched him for five hours and never saw him do anything.