It is this accident of coastal geography that brought archaeologists to the site in 1990, when the profile of a V-shaped fosse, a defensive or boundary ditch, became visible in the cliff face roughly nine metres south of the church itself.

The excavation, carried out in 1990 and published by Cotter the following year, uncovered only a short section of the fosse, about one metre in length, cut to a depth of around 0.7 metres and varying between half a metre and one and a half metres in width. What made the find more than just a drainage feature was the material inside it. The bulk of the fill was charcoal-flecked stony soil, and at the very bottom lay a thin deposit of charcoal mixed with fragments of burnt and partially burnt bone. Above the fosse, a single burial had been placed, suggesting the ditch had already gone out of use by the time the grave was dug. The fosse appears to curve toward the north-west, and the excavator concluded it may originally have enclosed the entire ecclesiastical site. If so, what survives near the cliff edge is a fragment of a boundary that once defined the sacred ground of the church as a whole. Such enclosures are a familiar feature of early Irish ecclesiastical sites, typically marking off the sanctified inner area from the land beyond, and sometimes incorporating earlier activity whose precise meaning remains unclear.

The site sits on a tidal island, which shapes any approach. Access to Skeam West depends on sea conditions and local knowledge rather than a signposted path, and the proximity of the archaeological remains to the eroding cliff edge is itself a reminder that what has already been found may represent only part of what was once there.