I see you are from Texas. Whatever method you use be careful not to cut off new growth (looks like fingers coming out of ground).
We cut back, a lot of it in our area, liriope with string trimmers. Work from the outside-in (so clippings are thrown into cut areas and you can see what your doing as you work through the liriope). Always keep the trimmer head positioned away from the house or anything (car, person, etc.) you don't want a rock or object to be thrown towards.
As long as no new growth to contend with, this is the fastest method for us.