In a field of well-drained pasture in County Kildare, there is a shallow rectangular hollow, no more than half a metre deep, that locals still call "the decoy". The name preserves the memory of something considerably more elaborate: a duck decoy pond, a type of managed waterfowl trap used in Ireland and Britain from the seventeenth century onward. These installations typically combined an artificial pond with a series of curved, netted channels, known as pipes, into which wildfowl were lured by trained dogs or tame ducks and then driven toward the narrow end where they could be caught in quantity. What survives at Coolsickin is the ghost of one of these structures, flattened to almost nothing, recognisable now only as a depression in the ground.

The decoy does not appear on the first edition Ordnance Survey six-inch map from 1838, which suggests it may already have fallen out of active use or simply escaped the surveyors' notice by that point. By the time of the 1939 revision, however, a substantial square enclosure of roughly 105 metres on each side was clearly visible, defined by a broad bank that widened at the centre of each side, a feature consistent with the earthwork infrastructure that supported a working decoy. That documented presence in 1939 makes the subsequent loss all the more abrupt: by 1972, the site had been levelled, with bulldozing operations recorded in the area. What remained after that clearance was the faint hollow that persists today, somewhere between four and six centimetres deep across its rectangular extent, still known to people nearby by its old functional name.