I'm guessing the end of the leash was used because you've kinda ruined/misused (sorry no offense meant), the prong/pinch, ecollar, choke, positive only, etc...(your own admittance "I've tried everything....").
I've seen the leash used like this as punishment. A fast, quick, wrist flick, of a smack with the end of leash. The key to your story is "I have to say it did work. and i have never seen Cody behave so well with another large dog." If what your saying is true "he's trained and placed many dogs in local law enforcement agencies"...this dude has more experience than some strangers on an internet forum.
You've exhausted all your options..you found something that's working...your dog isn't walking away ruined or hurt or abused...actually, he's walking away better than he's ever been (your words) and yet you go to the internet to see what strangers say. I just don't get people...I really don't.
I hope Bailiff comments (as he deals with pets/owners all the time of similar situation). You can use ANYTHING as punishment...hand, stick, ecollar, etc. It's the fair punishment, paired with the other reinforcers of the proper behavior, that get's you improvement. A lot around here don't like punishment, and don't like to talk about it or consider it as an option (or that pretty much any object can be used). No matter how much it's been proven (as long as it's fair and paired with the reinforcing behaviors/rewards) to work.
Good luck, OP.
"An excess of size is an unserviceable feature for breeding, his powers of endurance, his speed and the smartness of his movements suffer in all circumstances. Giants are never nimble."-Creator of GSD
Last edited by DaniFani; 05-20-2014 at 08:26 PM.