The drought in the gulf coast is causing the layer of clay beneath the house to shrink and my house slab is developing cracks. Also, the roots of the large oak trees nearby may be contributing to the problem. Does anyone know what to do about the roots - how do I kill them without killing the trees? How can I stop them from growing back? I hear I have to dig a trench around my house and kill all the roots growing towards the house. Also, I would appreciate any tips on finding a reputable contractor to deal with this.