I took the pooch up Gordale Scar last May- he's small, but weighs 18kg. He was also wearing panniers at the time and I had a full backpacking pack on - about 13kg, I suppose. The dog seems to enjoy a bit of a scramble but experience with previous doggies indicates that they have a forward-planning deficit and can easily fall off stuff. A Labrador would pull you off if he fell off, I suspect. I've trained Lucky to stay wherever he is on the command "Wait!" so that I can climb past him and pull him up any awkward bits. A long training lead is a useful thing for doggy scrambling and can be used on a harness to hoist the dog upwards, or downwards. Dogs need to get used to this sort of thing, though. A panicking dog pedalling air is not such a good thing and a dog falling off from above you could be disastrous. My previous doggies have managed Gordale Scar and other scrambles, up to about easy Grade 1's - Striding Edge (Birkett has it graded as 0.75!) probably being about the limit. All my doggies have been much lighter than a Labrador, though. I'm not sure that taking a lab up there would be entirely safe unless you were actually belayed at the top and could hoist the pooch up on a long line should he become detached from the tufa.