One scaled the walls of Guardbridge and Carnock, followed by a duck (5)
I believe the answer is:
gecko
'one scaled' is the definition.
I can't judge whether this defines the answer.
'walls of guardbridge and carnock followed by a duck' is the wordplay.
'walls of' means to remove the middle letters (the external letters or walls of the word are used).
'and' means one lot of letters go next to another.
'carnock' becomes 'ck' (I can't justify this - if you can you should believe this answer much more).
'followed by' means one lot of letters go next to another.
'a duck' becomes 'o' (resembles zero - 'duck' in cricket).
'guardbridge' with its centre taken out is 'ge'.
'ge'+'ck'+'o'='GECKO'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for gecko that I've seen before include "one climbing the walls?" , "Lizard than can't blink" , "Cold-blooded creature" , "Nocturnal lizard" , "Type of lizard" .)