In GENERAL, Petsmart trainers aren't always the best anyway. That's a whole different subject. My dog just graduated from an Intermediate class, but my trainer was sooo not the average Petsmart trainer.
Coonhounds can be difficult. IF you have tried leash training methods and followed them to a T, and nothing's worked, then you have to try something else. USUALLY, it's not that the methods don't work, it's that they weren't used correctly.
However, my dog that just graduated Intermediate is one of those who could not be leash trained, and I've been training for many years. I use a Gentle Leader on him, and I SWEAR by them. I LOVE them and have recommended them to numerous people with difficult dogs--and they always work. Only met ONE dog who could not be trained with a Gentle Leader alone, and she was a deaf pitty who needed the GL AND the turn-around method.
Gentle Leaders are WONDERFUL. They come with a training DVD and training manual. If you READ the manual and watch the vid, then follow it EXACTLY, you can teach your dog to walk perfectly with this. They do not like the GL at first--it's just like a puppy's first reaction to a collar. They scratch and try to get it off. They fight it. The training manual and the DVD describe exactly how to handle this. Abrionline.org also has some great vids on training with headcollars(GL).
Another thing that you have to keep in mind is that YOU MUST BE CONSISTENT. You have to stick with it or your dog will be dragging you around for the rest of her life. 9 times out of 10, the problem is not the dog--it's that she's gotten away with it just enough times, that she knows she doesn't HAVE to listen to you. Please do not take offense to this--this is just typically the issue with most dogs. Anyway, the GL would probably help you a lot. Petsmart carries these. The Halti is a cheaper version, but I DO NOT like them near as much. The GL has a clip just under the chin that makes it hard for them to slip out of. The Halti does not, and dogs get out of them very easily. And the Halti doesn't have the DVD. With both of these, the dog can still pant, open their mouth, drink, eat, whatever. So don't assume it's a muzzle just because it goes around the mouth--I constantly get that reaction with my Zeke, who uses a GL.