Blender: how to keep the feet on the ground?

Hi, I am really struggling with my idea of an animation. Simply described fpor the first testing animation the sim should do some squads. In Blender when I move the whole sim with the bone b_ROOT_bind_ it simply moves the whole sim without buckling the knees. So I buckled the knees but this makes the feet move up. So I need to adjust the position of the whole sim in Blender on the z-axis again to bring the feet back to point 0 of the z-axis. But the feet moved in their x- and y-axis coordinates as well. With every move of the body the feet move as well - which is not the case when you do a squa or for example you do a dance.


The next idea would be some sort of dance animation and I really do not know how to fix the feet in Blender on a ground position so that they do not move even when the rest of the sim body moves in any direction. This takes me so much time to finde the correct position for the feets again so I hope there is any way to achive that. 

I am a total noob to Blender and wnet through some tutorials. I think it might be solved with some "Inverse Kinematics"?! I used this for the knees so that I can move the knee and in that way the whole leg. But I do not now how I could achieve it that the sim body can move without moving the feet?!