As mentioned above, Russian tortoises can tolerate conditions fine, as long as they can burrow and do not become soaked. In the wild, they probably achieve this by burrowing into slopes, so that the rain doesn't get into their burrows (please see my new thread, "Ecology of the steppe tortoise in the wild" for more on this topic). In a backyard, I would think that you could use a doghouse-type structure to cover the area where the tortoise burrow. As long as they stay dry in there, they should be fine.