Is it possible that Alexander built the Castle of Cumnock, Ayrshire?
Patric Dunbar De Comenagh married Marjorie Comyn, one of Alexander's daughters and held the seat of Cumnock but I can't find any other connection of Patrick before 1296.

Cumnock Castle sat in the middle of Black Loch, the source of the Nith. The river Afton flowed into the loch and Glen of Afton was a main route over the Southern Highlands to Kirkcudbright. The castle would have been of strategical importance to the constable of Scotland.

This would explain the name Comenagh.