Haven't heard of a ha-ha here but I've always loved the combination of idea and name. Our closest equivalent would be a cattle gate. It is a ditch about a meter deep crossing a road in place of a standard gate. There are round pipes set in the top perpendicular to the road about 4 inches apart so that cars can rattle across without stopping to open and close a standard gate but the cows are afraid to stepp on it and won't cross and escape.