If you want to improve balance and strength in the leg muscles, try the single leg deadlift (also called the single leg Romanian deadlift). This exercise is primarily going to work your hamstrings and butt. The single leg deadlift comes with a high degree of difficulty because it is performed on one leg. An advanced level of balance and muscular control is required for this exercise. Here are the instructions:

Stand with a medicine ball positioned near your thighs. On one leg, bend down to lower the med ball near your ankles. You can bend your leg slightly, but try to keep it locked into position as you bend down. Your back leg should kick back as you lower the ball. Return to the starting position. Repeat the exercise on the opposite leg.