Between you, me and the gatepost

This expression signifying that something is said in confidence is sometimes in the form of “between you, me and the bedpost,” which is not always appropriate if the person being addressed is someone you are not intimate with. There are many variants where gatepost is substituted for fencepost, lamppost, garden gate, these four walls etc. Posts of some sort or other seem to be more favoured. The expression in the form of ‘gatepost’ dates from the 18th century while the others follow on later.