First good job at trying to dig out all those yucca roots - it is hard to get each bit of root but if root sprouts later this summer just dig down and remove it as well. If you like the spiky look of yucca try planting the area with phormiums or cordyline. Neither are as invasive as yucca and come in different foliage colors. The yellow variegated yucca is not as fast growing as the green yucca and growing yucca plants in containers can keep it under control. For a larger area I like Cordyline Festival Grass because the tall spiky leaves are a deep red color and it has a looser more relaxed growth habit. Keep growing, Marianne Binetti