We also spend a lot of time in a horse stance for the reasons mentioned below. To work the legs another one I really like is the rope. We hang a rope across the mat, about 50 feet in length at about 4 or 4 1/2 feet up.
Then we put together combinations, strikes, kicks, blocks, cross under the rope, using your legs, not your back, keeping your hands up to protect your face, come up on the other side do the same combination but with opposite hands and feet.
Go up the length of the mat 10 or 12 times and you've got a sweat going. You can use your imagination on the combinations.