The only evidence of its existence came from the air, when an aerial survey in July 1989 captured a cropmark revealing the outline of a circular enclosure roughly 55 metres in diameter. A fosse, the defensive ditch that would once have encircled the interior, had been ploughed flat over the centuries, but the buried soil disturbance still influences how crops grow above it, producing the characteristic variation in colour and height that aerial photography can detect.

The enclosure at Sleemana belongs to a class of site common across early medieval Ireland, where ringforts and similar enclosed settlements once defined the rural landscape in their thousands. Most surviving examples retain at least some earthwork above ground; this one does not. The aerial image also hints at a possible annexe extending to the north-north-east, a secondary enclosure that would have served as a space for livestock or storage, a fairly typical arrangement. To the south and north, further linear cropmarks on an east-west axis are likely the remains of levelled field boundaries, suggesting the enclosure sat within a wider pattern of managed agricultural land. Together these traces sketch a small, self-contained farming settlement, ordinary enough in its time, now entirely absorbed into the fields around it.