You can do this. Without any special leash or training aid. You have to show the dog what you expect, what you want. It will work better than just using pain, shock, and strength to keep control. You can use special collars and other rigs to pull the dog away from things you don't want them going for all day. They'll never get it until you actually show them what you DO want them to do, how you DO want them to behave. "Just because I can't get at that squirrel or that one other dog doesn't mean I shouldn't try again later, or go crazy soon as they take this thing off me!!!"
I just started seriously leash training the pitt/rott mix I recently bought home. Before, we fought tug-of-war with the leash and it made no difference. She charged after everything she saw continuously.
I did some research and talked to other owners. I took a set of techniques and tweaked them so they work for me. Just within a few days of using them, I've seen a tremendous change in the way she behaves. From straining to get at every single distraction she passes and turning it into a leash tug of war, to staying at my side and keeping focused on the walk.
1) It begins in the house. It's a process. At each step they should understand that they follow your lead or wait for your command, they don't just charge ahead. Whatever we do, we do with discipline. Start putting the idea in their head before the walk even begins. I'm not chasing you, I'm not wrestling, I'm not running to keep up. My dog sits when the leash goes on. Before she learned, there were times when I had to grab her butt and put it on the ground and make her stay still because she got so excited when she knew we were going out she wouldn't control herself and listen. But she eventually got the message. I'm not trying to secure the leash while she goes crazy. If she's acting up, I'm standing upright and not acknowledging her till she sits calmly on her own. Believe me, it works.
2) My dog is being taught that an open doorway or a stairwell is not an invitation to plunge ahead. I open the door, and we contemplate the open door without going through it while she sits. She doesn't go through until I give her a command or go first. I step outside the door, and invite her to follow me. Then she sits while I close it and lock it. Then we go down the walkway to the front stoop, where she has to sit and wait again while I go first.
3) We start the walk. And this is the important part. When she goes charging ahead, I stop. When the leash goes taught, I tug back just enough so her butt naturally sinks to the ground and she sits. She doesn't move again until I move. If she tries, I sit her down again. While she is still, I take a VERY deliberate step to get beside her. The side of my leg just barely touching her chest. I stop, I 're-set'... let her get a sense of how we're standing together. Then I start walking again. I do this EVERY TIME she gets ahead of me and starts to pull. It's VERY important to be deliberate in putting yourself beside the dog where you want to be while you walk and taking a second to just stand there like that and let it sink in so they begin to learn the natural order of things.
What you've told the dog is you stopped because something was out of whack. But then once you fixed it and she was waiting patiently it it was time to go again. You may feel dumb doing this, and you may be out walking for awhile without getting far. But it works if you're consistent with it. If you're sitting around not doing anything, take the dog around the block. PRACTICE WALKING. Don't be put off by the fact that the dog just charges ahead again as soon as you start moving the first several times. Alot of people try it and give up when they don't see an immediate change. It takes some time for it to sink in. Remember, when the dog steps outside the house, in THEIR mind it is their opportunity to do their own thing. And to lead you over to each distraction they want to explore. You have to teach them over time that this is not their turn to do things on their terms. You have to communicate to them what you expect, and that doesn't happen in five minutes.
4) PAY ATTTENTION when you walk. See the distraction before your dog, see their head suddenly swivel. Recognize that they're about to lunge for it. As soon as you feel the dog tense or see their head swivel, give a quick, small, gentle tug of the leash. Get that head to swivel back to you or straight ahead. You may have to do it a few times but they'll soon forget what they were looking at and focus on the walk again. Easier to recognize the signs early, do a quick, SMALL leash correction, and keep your dog moving. If you're not being attentive and you suddenly find yourself trying to pull your dog back from a fully tensed lunging stance, you've already lost. Even if she only weighs 20 pounds and it's no struggle for you to pull her away. It's now a tug of war, a battle of wills. She doesn't understand what you want anymore because you let her put the focus on the distraction when it should be on the walk. You can pull her away from THAT issue, but to her it doesn't necessarily mean she shouldn't chase after the next thing she sees. It just means you didn't want her focusing on that one specific distraction. But there are a bunch more coming next, and she'll go after them all until you teach her to focus.
If you keep it about the walk, keep the dog focused on straight ahead, they now understand what you want. Which is more important than them understanding what you don't want.
5) Praise them verbally when they do well, the same as when they come, sit, or stay on command, then stop the praise when they pull or lunge off course.