Brunette Girl Shows Off In The Wooden Barn

To "lock the barn door after the horse has bolted" implies that one has solved a problem too late to prevent it.
"Were you raised in a barn?" is an accusation used differently in various parts of the English-speaking world, but most commonly as a reprimand when someone exhibits poor manners by either using ill-mannered language (particularly if related to manure), or leaving doors open.
"Your barn door is open" is used as a euphemism to remind someone to zip the fly of their trousers.