More than a week of rain
In the time of the pony express, the men said the pony ran in all weather. Dogs will work in rain too. Especially sheep dogs. Sheep are not smart at all, they tend to head for the low dry ground if separated from the flock. Flash floods would kill them without the ever faithful dog.
By no means am I saying to risk your health. I am simply reminding all to remember the importance of keeping your dog active. Treadmills are a great option for rainy days.