My dog, Rover, was mentioned one of the older gritstone guides as 'a fine climber', but I think his hardest solo was 'Disappointment' at Agden Rocher which was V Diff at the time but is described in the latest guide as a 'dirty gully' (still V Diff however).
Rover can be seen in this picture patiently waiting his turn on Crewcut at Millstone http://www.ukclimbing.com/images/dbpage.php?id=109046
One of my dogs once ran up a 5a UK tech grade slab boulder Problem at the Roaches, but he had Trained on the bottom half of the easy way down at Wintours Leap Several Times before that.
The Swanage pioneer Richard Crewe had a spaniel, while it was a competent mover despite it´s stupid ears and stumpy legs my border collie was far the better climber. On the right route HVD was doable. Richards dog was trained to sit in a rucsack while he jumared out so you might meet it bounding along the bottom of the Boulder Ruckle on a good day!