If that's the way your client sees their dog, Julian, then that's OK. As it's a recognised breed, you can trawl the Internet for other dogs to provide detail. I'd be wary of reproducing the gum and teeth detail too faithfully - been there, done that, not popularJulianC wrote: It's years since I've done a dog portrait! Do you think this photo is good enough? And if so, what would you do with the grass?
Hmmm... is the field on a slope? Or is the camera tilted? Looking at the leaning trunks of the trees, I'm fairly confident the field is flat, and the photo rotated. Rotating it back to level gives me a better feeling for what I could do with this. As for the grass... I think you have to include some, if only to account for the dog being on a "slope". Personally, I'd draw the dog first, leaving white blades where the grass overlaps. Then I'd expand the grass outwards (not necessarily in the complex way that it appears in the photo) until I felt the balance was OK. I'd also want to fade it away as soon as possible to prevent it from drawing attention away from the dog.
Also, I think this is a hay meadow and the dog's laying on cut grass. Personally, I like the grass to the right of the dog, and I'd favour repeating that to the left... but you can't - because the hay is bunched up into a mass that's hiding the belly and rear leg.
That said, if you rotate the photo anti-clockwise (as I did above), so the tree trunks are upright, I think you'll find the grass to be much less of a problem. You can pull more detail out if you sharpen it. And, as you can see above, I think it looks OK when rotated back to a level horizon, which causes fewer problems with the hay.
I hope that helps.