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"You do three pull workouts and three push workouts three times per week, using different exercise at every workout. While you can use any exercise you want, when possible I like to use 2 multi-joint exercises and 1 isolation exercise.
For example, our first hamstring workout of the week might consist of Romanian deadlifts while the second might consist of lying leg curls. The third hamstring workout of the week – the isolation move – might consist of glute ham raises."
CT's program is a sample template. Unlike other programs on here you can makes some changes.
I'm doing front squats, squats, & reverse lunges for my 3 push days. RDLs on pulling days. I'll probably mix in leg curls when I can but I feel like RDLs are more applicable to real life than leg curls. Other hamstrings exercises that don't require the machine are barbell hip thrusts, Nordic hams (AKA glute/ham raise without using glutes), single leg RDLs, standing leg extension/Curl with a cable attached to the ankle, cable pull thrus, just to name a few.
If you need more quad ideas then your split squats would work. Leg Press, lunge variations, squat variations, pistol squats, and so on.
The nice thing about a bodybuilding program is that the goal is to stimulate the muscle so you can use variety. Strength programs require you to stick to the specific exercise that you're trying to improve.