Toddler: correct them with a similar sounding word "Wheres the truck?"

Kinder years: I go the dramatic over reaction. Not yelling and screaming. But lots of gasps. Looking around and making sure no one heard them. Completely freak out.

School age: I threaten with only ever being able to watch in the night garden and all music will be confiscated as that is obviously the cause

My children have never said anything worse than "stupid" past the age of 2 before that it was the occasional mimick. This works. Preventative is better than cure. And even though stupid isn't that bad I still did the dramatic reaction. Worked a treat. I swore more than my daughter does at her age DD freaks out if she hears a young person swear lol.

I don't like ignoring because I don't find it works.