A proverb meaning you cannot stop people from talking; rumors and gossip cannot be completely prevented.
どんなに説明しても、噂は消えない。世間の口に戸は立てられぬとはこのことだ。
No matter how much you explain, the rumors won't disappear. This is what they mean by 'you can't stop people from talking.'
有名人はプライベートがすぐに公になる。世間の口に戸は立てられぬから仕方ない。
Celebrities' private lives become public quickly. There's nothing you can do — you can't stop people from talking.
あの事件のことはもう忘れたいが、世間の口に戸は立てられぬので気をつけた方がいい。
I want to forget that incident, but since you can't stop people from talking, it's better to be careful.