This is almost always caused by inadequate watering. If the soil is moist, it won't shrink and crack open, and so the wasps can't make their nests. If you know where the nest is, you can lay the hose there after dark, and turn it on low, allowing the soil to expand and destroy the nest.
Wish that would work, but I live in Colorado - semi arid here. You can flood the yard one day, and the next day the cracks are big enough to loose the dog in. Oh well. I'm in for any other ideas - I dont know whether to call an exterminator or an exorcist. Doesn't help that we have stone facing on the house either.