My Border X Heeler has doggy aggression too stemming from really poor socialisation when my hubby had him as a puppy. We did the one on one training, which was great, but he was only fine when the trainer was there. When our own, Roggie just went back to being the same old barky leash-pulling anger hound.
We then put him in a fast-track obedience training kennel for a week, came up a treat while with the trainer, but then reverted back to his old ways with us.
It was then that we figured out that it was probably an issue with us handling him (I can see the doggy trainers all nodding their collective heads in agreement there!).
We're now in group training with ADT here in Melbourne, which caters to problem doggies & they give you specialised attention when your dog is being a real pain in the bottom (as Roggie so frequently likes to be!). However, each time we see a different person, they each diagnose Roggie with a different aggression type. I've given up on people diagnosing Roggie, all I really want is good tips on how to manage his behaviour when he is being Mr Aggro 2007 because ultimately, it's down to me as his handler (or my husband, as *he's* the one that's caused the problem & *he* has to fix it...arrrgghhh don't get me started!!!) to control & manage his behaviour, simply because whether it's fear or any other type of aggression he looks up to me to lead him & let him know what behaviour is acceptable.
So far, it's been a really long road full of ups & downs, good days & bad days, and people at dog parks giving you the evil eye because you're trying to correct your dog as your trainer told you - which can sometimes look really heavy handed when correcting with a check chain *sigh*
Anyway, I feel for you, I know how frustrating it can be when all you want is a nice walk with your doggy and instead you spend most of your time being yanked around by an over-excited dog hellbent on eating the oodle across the park.
Good luck!!