As I was watching the PBS show Mystery! this past Sunday, they referred to a ditch between the road and field as a “ha ha” - which has stuck with me since, making me giggle at unseemly times too, I might add! Was this (or is this) an accurate term, in the British countryside? Or is it something they made up, or something that has fallen out of use? Mrs. Bradley’s (Diana Riggs’ character) chaffeur kept calling it a trench, but Mrs. Bradley kept correcting him that it was a “ha ha” – to keep people off the lawns and away from the sheep, or something to that effect.
Yes, there are such things as "ha ha"s. Essentially, they’re ditches to mark edges of territory and to stop people, sheep and cows wandering about willy-nilly. Often found boardering posh estates, hence Mrs Bradley being proud of her ha ha.
A photo of Ha-Ha Road is shown on this site (scroll down almost to the bottom of the page):
Back to the OP: yes, they’re fairly common in the UK, particularly in grand estates. By using a ha-ha, the nobility would be able to sit outside and look over a pastoral landscape unbroken by ugly walls or fences, while not having to worry about livestock coming up and nibbling on their cucumber sandwiches.
Ha-ha’s were originally carefully designed so that the land on one side of the ditch (the manor estate side) would be higher than the surrounding land, this would render the ditch itself virtually invisible to the estate owner.
Sometimes there would be a fence or hedge on the farmland side of the ditch, which would also be near invisible too.