out growing leg machines?

ok, for too long of a time now, after heavy sets of squats on leg day, when i do leg extensions and leg curls i can max out the weight and do like 20 reps. So when you out grow those machines, how do you work out those muscles in your legs? Lately, i just have someone give me extra manual resistance, but i figure their has to be a better way.....?

i get the aerobic dumbells, the 10lbers and stack em on top.....

Are you cheating? Or is a slow and controlled movement? You can add a plate ast daiblo2185 suggests or you can go all negative reps.

i will try those ideas out today