Griffin wrote:
Do they only come out in fog or does the fog come with them?  Are they intelligent or is it by mere instinct given them that they protect the earth?  You say they are protectors of things, in what way do they protect?
The fog comes with them, though that's not common knowledge. Their sentience is undetermined but I see them as more soulful than intelligent if you understand my meaning. The protective role is an instinct. Hm...in what way do they protect...it largely differs on the type of leukothere and what they protect. For instance, the white stags protect wildlife right, that's based on legends that say they only appear to hunters who risk overhunting a certain area or creature and lead the hunter off in a wild chase that exhausts them and causes them to forget their original hunt for a time until the balance is restored. There are also legends telling of how they similarly appear to wayward travelers that wind up chasing them until they disappear and the traveler realizes that they've either reached their destination or the way to it. 
White hounds serve kind of a guard dog role for the earth's secret places. Some think that they guard places of great mystical power, others the sites of hidden treasures, and still more hold to a view that they guard both. None are really sure. The white hound ancestor of the ghost hounds was said to haunt a sacred mound, which is where the ancient Sidhe is said to have encountered it and somehow won its friendship. No one knows what was so special about that mound.
White boars are similar to the Tree Drakes in that their main role is more like gardener than forest warden. There are a handful of obscure rumors about overzealous woodsmen who were chased out of the forest by large white boars. Mainly though, they appear once in a very great while to tend the trees and plant life of the forests. It's generally assumed by the Dryads that they do this semi-regularly but are rarely spotted by anyone.
White bears are not even known of by the majority of the races in Fantasia. But the legends of those few mountain-dwelling people that do tell of them seem to portray them as the earth's protectors of people that roam the mountains in a fashion similar to the rescue dogs of the Swiss Alps. There are many tales of those who bind a white bear to themselves through their musical prowess and earn the lifetime protection of the white bears. In some tales the bear would appear whenever the individual was in danger or threatened, in others the bear became the person's constant companion throughout the remainder of his or her life. There are even tales of the latter strain that tell of the bears remaining with the particular person's family even after he/she passes on. Like the white hounds, they are more soulful than outright intelligent, though they seem from the tales to be very adept at understanding people.