SLDL's are one of my favorite exercises. Though, at times, I prefer Romanian DL's as having a better focus on the hams. Also hits the lower back better, for me anyway.. Throwing GM'ing into the mix of 3 great exercises for exceptional ham, glute and lower back work. Take your pick and see what works for you.
The regular DL and squat can improve, almost overnight, when these movements are done with serious intent. Would still suggest adding a regular ham curling exercise, to follow the function of the ham's themselves. Like standing leg curls. Or lying face down on a bench, have someone wrap a towel, belt, etc, around the ankles and have them apply resistance as you curl your legs up. Can also use negative force, resisting all the way back down to the starting position. Exceptional movement. Good Luck. .