Fairy Rings in my Lawn

I have Fairy Rings in my lawn. It conjures up images of little fairies dancing in a circle in the middle of the night. That is actually the superstition that contributed to their name. They are circles or arcs of lush, dark green grass that are caused by the release of nitrogen by a class of fungi called Basidiomycetes that live in the soil. The rings can be anywhere from a few centimeters to 20 meters in diameter. They appear after an extremely rainy period and become larger each year, growing up to 1/2 meter per year. But they cause no serious injury to the lawn. They just keep on expanding until they run into a barrier.... or they make it into the neighbor's yard! There are three types: just grass like the one I have, grass and mushrooms, or just mushrooms. The mushrooms may or may not be poisonous so if you have kids or pets you need to be vigilant and remove them. You can get rid of them by removing the soil to a depth of one foot and two feet beyond either side of the rings. Then replace with new soil and reseed or lay sod. But if you drop any of the contaminated soil onto a healthy area, it will start over again in that area. Since mine is just grass and it isn't hurting anything, I am going to leave them alone. Besides, I wouldn't want to disturb the dancing fairies!