Last week, we considered whether lower body strength can be improved efficiently without heavy weights.
The sad answer is "Not really." Only moving the heavy weights can improve strength efficiently, but some calisthenics can at least maintain strength, prevent muscle decay, and maybe build a little strength too if not just muscle endurance.
That post mentioned some of those key lower body exercises.
Below the fold, good video tips on often-neglected Side Lunges and correct technique for Body-Weight Squats (We believe in "Ass To Grass").