Ha-ha n. : A sunk fence; a fence, wall, or ditch, not visible till one is close upon it.

Example:
How to increase breast size naturally ha ha?

Taxonomy
grounds, a ha, walls, Chinese, free encyclopedia, grills, ha-has, Kew, Double-sided, barriers, Royal Artillery, Lunatic Asylum, European origins, Horace Walpole, country, ditches, farm, walks.

Defination from the web:
Ha-ha is an expression in garden design that refers to a trench, the inner side of which is vertical and faced with stone, with the outer ... The ha-ha consorted well with Chinese gardening ideas of concealing barriers with nature, but its European origins are earlier than the European ...