From what I've read here I'm guessing that your horse just simply doesn't understand lunging. It's quite possible that he's never been on a line before and you're asking for things that he just can't give.
Lunging can be VERY taxing on an out of shape horse. (not to mention potentially dangerous to tendons and muscles) You wouldn't pull a pasture puff off their knee high grass and ask for a 15 sec barrel pattern would you??? I know you won't find my butt in an intense aerobic class at the local gym!!!!
Remember that a thin-to healthy weight horse can still be out of shape...it's not just the fatty mcbutter pants horses that need conditioning.
Slow down, ask for some hands on local help, try a few weeks of walking on the line...will he/she do that?? Verbal commands for Walk, trot, & canter are going to be VERY helpful. Tho not necessarily "needed". I'm urging for you to get local/ hands on help because I think that proper lunging is next to impossible to teach on the net because you need to be able to read the horse and any advice we give you will be nothing more than educated guesses without being able to see the horse in action.
Kevin is right, you don't want a tie down. You don't want martingales. You want results and that means breaking this communication barrier down to the basics and starting at walk.
Good Luck and keep us updated.