The ha-ha may have originated in deer parks during the 18thCentury. In large lawns and gardens sheep and cattle were useful to keep the grass at a manageable length but problematic if one wanted to keep them away from the ornamental areas of the gardens and the out of the house. A ha-ha served to prevent animals from accessing certain areas of the gardens. A trench was dug into the lawn and one side reinforced with a stone wall. Because the trench is below ground level, the barrier created by the ha-ha doesn’t interrupt the sweeping view of the landscape. A good ha-ha is not visible until one is right next to it. This might cause one to exclain in surprise “ha ha” - hence the name.