Dont you hate it when you watch lungeing videos of unbroke horses and they just take off in the round pen and start lungeing a perfect circle? I think it has ALOT to do with your energy and position. I had the same problem with my mare, I would try to get her to move forward, but she knew I didn't believe in it and that I wouldn't follow through. she would just eat grass and ignore me. My trainer would just walk in with nothing in her hands (she does VERY minimal hands on with her, its mostly verbal instruction) and Frida would just take off. When I eventually got her going, she was SO POKEY. So that being said, I think if you walk in with the confidence to move your horses feet, and position yourself in a manner that has maximum effect, it will work. You basically have to throw forward energy into the horse, and plant your feet into the ground even when walking. Our first month lungeing I was out of breath it was so much work and concentration, and now, now I can stand fairly still and relax more. I started out keeping pace with her, with my outside shoulder facing her withers, my lunge line hand against my hip pushing the energy through the lunge line and the whip pointing towards her shoulder. I used to just go full force with the theatrical slashing of the whip (NEVER touched her) but then I realized it was more beneficial to build-up to that point (and now find I rarely need to) I would cluck, then give a verbal command, then swish the whip on the ground, and then if that didn't work build up the intensity. You just need to win the right to move her feet in her mind. Good luck, you'll get it!