Moshe it depends on their purpose, and you've said it is not possible on the day to arrange backgrounds. That would be worth the effort - even waiting to capture the dog against all-pavement or all-grass would be better than the bisecting lines. It is a fine line between a candid and a portrait. Are any of the dogs your own? If not - yes it can be difficult sometimes to take charge when you are shooting another person's dog.

It is probably better to put a couple of shots into the thread rather than just give a link to them, makes it easier for people to take the time to really look at them.