The overall instructions indicate "Three unclued solutions of 13 letters are of a kind referred to in the clue to the fourth one.
Solutions 1 English setter
Solutions 2 Cocker spaniel
Solutions 3 Scotch terrier
Clue 4 "Correcting say, a canine barking in training gets hard (13)"
Solution 4 appears to be "Straightening"
I can see some vague link to the solutions but would like some more profound explanation.