So when I first got my horse I did all my work with a lunge line. He is very well trained when it comes to knowing what he is suppose to do.. About a year ago I started just free lunging him in the round pen and he did a lot better vs lunge line. Well about 2 months ago he started getting lazy and he would start out perfect then after going around the round pen 2 times he starts to slow down and cross fire. I'd immediately threw my whip in front of him make make him go the other way into a lope until he did it again (i was told by a trainer I use to work for to do so, it worked really well with a horse that was brought in for training) Still no improvement! So I started last week back on the lunge line (I had gotten lazy myself and hadn't used it in about a year and a half) and he has no manners what so ever. Doesn't want to listen pays attention every where else etc. I got him to finally start listening to me with that so I moved him back into loping around (without telling him to trot, walk, or whoa) and he's still cross firing!
So after that long story my question is:
How can I get him to stop cross-firing on the lunge line most importantly?
2nd Is there anything else I can do in the round pen to get him to stop?