This must never happen again.

这种事再也不能发生了。

《牛津词典》

It was just a one-off; it won't happen again.

这事绝无仅有；不会再发生了。

《牛津词典》

It's frightening to think it could happen again.

想到此事可能再次发生就使人不寒而栗。

《牛津词典》

I want those reforms implemented immediately so that this doesn't happen again and so we can prevent future attacks."

VOA: standard.2010.01.05

Suppose the planet were hit by a comet-- this happened--something like this happened sixty-five million years ago, so it could happen again.

假设这个星球被一颗彗星击中-,这样的事，大约六千五百万年前,发生过，所以它还可能再发生。

耶鲁公开课 - 金融市场课程节选

And, again, I want you to look at this and think about what's going to happen here.

再一次的，我希望你能看看,这段代码并想想之后会有些什么。

麻省理工公开课 - 计算机科学及编程导论课程节选

An international convention was drawn up in 1948 to ensure that nothing like this could ever happen again.

BBC: [an error occurred while processing this directive]

The Bank said the close-down was a one-off upgrade and will not need to happen again.

BBC: News | The Company File | Millennium bugs bank

It pointed out a process deficiency that we fixed and it will never happen again.

WSJ: Boss Talk: GoDaddy Gets Ready for New Domains