Trim dog after dog (7)
I believe the answer is:
curtail
'trim' is the definition.
(thesaurus)
'dog after dog' is the wordplay.
'dog' becomes 'cur' (cur is a kind of dog).
'after' means one lot of letters go next to another.
'dog' becomes 'tail' ('tail' can be a synonym of 'dog'**).
'cur'+'tail'='CURTAIL'
(Other definitions for curtail that I've seen before include "Reduce in length" , "make shorter" , "Impose a restriction on" , "Dock" , "Reduce in extent" .)