Fastidious writer puts 'sheep' in a margin - wrong (10)

'fastidious writer' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see an association between them that I can't see?

'sheep in a margin wrong' is the wordplay.
I cannot really understand how this works, but
'sheep' could be 'ram' (male sheep) and 'ram' is found within the answer.
'a' could be 'an' and 'an' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

'puts' is the link.

Can you help me to learn more?