Lunging an aggressive horse?

This may get lengthy, hang with me please!

As you may have seen, I have a gorgeous palomino Quarter Horse, roughly 8 years old. I have been around horses for... most of my life, but real hardcore into them for the past 7 years. I have free lunged horses who know how to lunge in round pens before, about 5 years ago, and done fine. I'm pretty fearless when it comes to horses, but to an extent.

Anyway, my horse quits sometimes and someone suggested lunging, as it's a good stretch. I winced at that suggestion. My sweet, lazy tempered Dillon has this opposition to me lunging him. The first time I tried it was with a lunge line. (Note: I got him April 4th, 2013, by this point we were still getting used to each other and I didn't have half my confidence and Lead Mare personality as I do now.) He charged me and I flipped out, naturally. When I say charging, I mean ears pinned, neck stretched out, chest puffed out, charge. I swung my whip, hard, against one side then the other shouting at him fiercely. He reared 5 ft away and wheeled to the side, pulling the lungeline loose from my hand.

Anyway, I called my experienced super patient neighbor who doubles as my for-free riding teacher, she came over and made him lunge on that line. It made me feel better, because he charged her/pulled away from her a couple of times, but she backed him into a corner so he couldn't do that and after several charges, he also stopped that. She offered for me to bring him down to her place before riding so she could lunge him in her round pen. She did that and he responded so much better, no lunging, just extremely lazy. She got him to trot for a bit, but no canter. She then suggested we bring the round pen to our place, so we did. I, after hard work, got him to canter and trot and he lunged perfectly for about 2 weeks. Then, he resorted back to his old charging ways.

I got so fed up, not to mention the adrenaline rush in less than 10 seconds, and after 3 charges, I would take his halter and walk around, 20 minutes on each side, sometimes making him trot. He was irritated and resisted slightly, but did it. I eventually realized he wasn't acting as anxious and high spirited on the trails, so I stopped lunging him. Until he started his new things of quitting. That being said- I use a crop with him, I'm not afraid to whip him, and I'm open to suggestions. I want to do what's best for my horse, and I want to become a better equestrian. Thanks! :)