Richard
I assume you have seen the 1911 Census record - the family name was recorded as Gardon
http://www.census.nationalarchives.ie/pages/1911/Londonderry/Londonderry_Urban__2_/Bishop_Street/601995/

On the 1901 Census he was a single man.
http://www.census.nationalarchives.ie/pages/1901/Londonderry/No__3_Urban/Newmarket_Street/1529972/

One of my relations Leonard Fieldman married Pauline Frais  in 1944 in Belfast. Pauline's mother was Rachel Gordon and her parents were Reuven  and Yetta Gerber both born about 1866 in Russia
Hope this helps
John Edwards