Fergus and his family were remarkable ecclesiastical patrons, working with Augustinians, Benedictines, Cistercians, and Premonstratensians. Surviving charter evidence reveals that Fergus granted the lands of Dunrod, St Mary's Isle (upon which a priory was at some point erected), and nearby Galtway to the Augustinian abbey of Holyrood. A fifteenth-century list of properties belonging to the Knights Hospitaller reveals that Fergus had granted this order of the lands of Galtway (within the mediaeval parishes of Balmaclellan and Dalry) at some point in his career. This transaction appears to further evidence Fergus's alignment with the English Crown.