Fallon now cuts down all of the rose bushes in the cutting gardens at Garden Valley Ranch to 6-12" several times a year. As soon as one flush of blooms ends, she chops them down to nothing and they produce roses for bouquets with incredibly long stems soon afterward.
She discovered the method in much the same way as your Weedwhacker experience. The deer came onto the property and chewed the roses down to nothing. She cried and cried and cursed the deer, but subsequently discovered it was the very best thing for a cutting garden.