Unfortunately, there is no built-in feature that will allow you to disable sorting for a sepcific column. That said, you could:
a- Create a new style or template for the column's ColumnManagerCell that overrides the default behavior of sorting with it is clicked
b- Handle the SortDescription's CollectionChanged event to prevent the column's sort description from being added to the collection.
Technical Writer - Xceed Software
Of all the things I've lost, I miss my mind the most. - Mark Twain