The Collaborative International Dictionary
Sunk \Sunk\, imp. & p. p. of Sink.
Sunk fence, a ditch with a retaining wall, used to divide lands without defacing a landscape; a ha-ha.
WordNet
Usage examples of "sunk fence".
At the bottom was a sunk fence, its sole separation from lonely fields.
There was a sunk fence in front of the marquee, dividing the lawn from the park, but a temporary bridge had been made for the passage of the victors, and the groups of people standing, or seated here and there on benches, stretched on each side of the open space from the white marquees up to the sunk fence.
It had a small park, with a fine old oak here and there, and an avenue of limes towards the southwest front, with a sunk fence between park and pleasure-ground, so that from the drawing-room windows the glance swept uninterruptedly along a slope of greensward till the limes ended in a level of corn and pastures, which often seemed to melt into a lake under the setting sun.