I too train and love very high drive dogs. My current dog is an Aussie from working stock lines. She is 60 pounds so at the top of the weight for the group. I do a lot of physical exercising and conditioning with my dog as I don't like to see fat, lazy dogs especially when they could be really nice dogs to own.
So, as with most driven dogs pulling on the leash comes with the dog. I address this by making this a command or release. I use a standard harness, a nylon or leather flat collar and a prong. I don't own a chain. I make my own leashes except for the leather " dress" leash and tab. We have 4,5,6,8, 30, 60 and 90 foot leashes. Each has a use. The only time she is off leash is training in the ring and at home inside.
Our standard combination is the harness, flat collar and prong with the 8' leash and 12" tab. The leash connects to the harness. The harness has a connector to the flat collar, the tab has the leash running through it and is connected to the prong. We can walk loose leash, close order heel with the tab, or release with the command "sniff ". I started right out the first day with her on the prong and 12" tab. There is no chance of pulling. I rewarded every slack event at first. No matter how small. I also introduced her to " watch me" again reward every look at me, every check look at me. Very quickly she learned that keeping an eye on me was all good. She got lots of rewards and praise.
One thing about this part. Dogs like to look around and walking straight ahead while watching you is a bit foreign to them. It takes a while before they get comfortable walking while watching you. If you are military "eyes right" or " eyes left" while marching would be similar. Try it yourself. It's harder than you think.
We have a "right side" heel too which means she needs to watch looking to her left. This year I added " lead" and " follow " a bit more difficult with out pulling on the leash. She has to look straight ahead for these.
Back to pulling on the leash. I started with the tab. Not letting the leash out. Obviously she couldn't yank very far before the tab closed the prong. It's not a hard correction, true a bit negative, but these very high drive dogs have nerves of steel and really want to please you. At least that's my finding. It didn't take long for her to note that the rattle of the prong chain meant she was out of position and needed to get closer to me. No real correction here. I never use more than a finger tug, usually just wiggle the tab a little when necessary. At a certain place I offer a release for her to sniff and " find a spot" ( go potty ) during this time she is free to pull as hard as she wants on the leash and harness. I've seen her pull against the fish scale well over her weight so she can pull hard. It's good exercise as almost every muscle gets worked hard. My knee brace gets a good workout too.LOL When it's time to heel again I use our heel command. I revert to the German command here "fuss". And she quickly comes to heel position. I can either pick up the tab or just gather the leash and " walk nice". Just a side here, I also teach her to only start walking when I start with my left foot. When I start with my right foot it means I'm leaving and she is to stay in place. No command for either.
It does take a while and you need to be very consistant here because you are teaching multiple commands for just going for a walk. However this is a 3-4 times a day, every day event so it is very important. We live in a dog appt with some of the rudest people and matching dogs imaginable.
I never allow another dog to get even close to us. Never go to dog parks. I use lots of distraction with treats to prevent interactions. Sometimes we get caught in bad spots with no retreat possible so a stand in place is the best as it is not submissive or threatening. It often turns into a barkfest in a hallway but I always position my self between my dog and anything happening.
So, this is how I get around leash pulling. It's not my invention as an early trainer taught me this some 25-30 years ago. Some of my dogs have been more couch dogs and responded very quickly to this. The tab is the main point as the dog simply cannot not get a run at the leash without a command.
Tron GSD SCH III, AD, TD. Never to be forgotten buddy
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Samantha, Australian Shepherd, rescued , loves everyone