Can you please include birthyears when asking for lookups?  The 1851 census has 11 entries for the name Alexander Wood all of whom were born in Portknockie 
Submitted IGI entry shows birthplace as Cullen Banff  
ALEXANDER WOOD   Birth:  17 JAN 1812  Christening:  18 JAN 1812   Cullen, Banff,   
Father:  WILLIAM WOOD    Mother:  KATHERINE MAIR  
JAMES WOOD   Birth:  04 JUN 1814   Christening:  10 JUN 1814   Cullen, Banff,   Father:  WILLIAM WOOD    Mother:  KATHERINE MAIR  
Then there is this 1851 entry for Portknockie Banff - all born there
Alexander Wood 40 boat builder
Isabella 34 
Catherine  13 
Alexander  10 
William  7 
Isabella  3 
Rathven ED 5A Page  3 Line 9