It took me 10 years and a terribly wild dog to really "get it" about loose-lead walking, so hopefully you can learn from my mistakes and avoid a lot of hassles for yourself and the dog. Teaching dogs to walk on a loose leash at all times has almost been a dog-trainer's secret, because it's somewhat difficult to adequately teach in an obedience class situation.
But it's really not so hard, and your slip collar should give plenty of control after you've done this program for just one to two weeks. I know you don't believe that--I didn't, either!
Okay, here's the secret. Start for a walk with your dog, but forget about getting anywhere this time, and for the next week or so. Instead, keep your attention on whether or not the leash is tight. Do not wait for the dog to pull on the leash, because then both you and the dog will be confused by when lead tension turns into pulling--the distinction is just too hard to consistently recognize. Instead, make your criteria a loose leash.
Check the position of your arm that is holding the leash. Good control means your arm is bent, your elbow is in toward your body. A handler with the arm holding the leash stretched out as he or she walks along has far less control. With your arm bent, you also have the ability to briefly stretch out your arm as you make the maneuver I'm about to describe, giving you a moment of slack in the leash.
Okay, you step out the door and whoops, the leash goes tight. Our natural reactions are to pull or jerk back on the dog, to hold on uncomfortably as we go toward our destination, or even to go faster, letting the dog set the pace. Do not allow yourself to do of these things! Instead, choose one of three things to do. You can stop, abruptly change direction, or back up.
For puppies and soft dogs, stopping may be enough. For a large dog with an established habit of pulling, changing direction will probably work best. Backing up is a nice touch later on, when you and the dog have a lot of training, just to keep it interesting. All of these maneuvers tell the dog, "Oops, if I pull, I get there slower, not faster!"
Remember, your arm's normal position when holding the leash is bent. The leash has now gone tight. Quick (you want this to be a surprise to your dog!), straighten your arm to create an instant's slack in the leash, as you turn and take off in another direction, usually either to your right or back in the direction you came. The dog may feel a quick pop on the leash, but at the same time will realise that "Whoops, I missed a turn, I better catch up!"
Within one to two weeks, your dog will expect the leash to remain loose, because you will have reacted every time it goes tight. You see, we are the ones who teach the dogs to walk on a tight leash and to pull us! Pulling back on the leash creates a natural response in the dog to pull forward. Letting the dog cause us to go faster makes the dog think "Oh, this is the way to get where I want to go! I should pull!" And just letting the leash remain tight as we walk along is constantly telling the dog we want a tight leash, that a tight leash is normal. Jerking back on the leash may work to stop some dogs from pulling, but it is not a clear message to the dog, and will be perceived by some dogs as unfair and upsetting, to the extent that those dogs will become terribly confused.
See, all you have to do is be unpredictable, so your dog has to keep an eye on you to keep pace! The loose leash also causes your dog to pay more attention to you at all times. It keeps you and the dog from becoming dependent on messages through the leash, which are definitely second-best to messages coming from your body and voice. A loose leash makes all training more effective and more humane. The slip collar will give plenty of control with a dog and handler trained to a loose leash. Some dogs will do fine on a buckle collar, but a slip collar can be a good precaution against a buckle collar sliding over the dog's head in an emergency such as another dog attacking it. When kept loose, a slip collar is not obstructing the dog's breathing or causing other problems.
Though a well-trained dog becomes very sophisticated about keeping the leash loose, you will always need to remember to react to a tight leash with your changes of direction, lifelong. Anyone who just walks along with even a well-trained dog keeping the leash tight is telling the dog a tight leash is wanted, and it is important never to give this message. The reason dogs can learn to work on a loose leash in one to two weeks is that it really wasn't a dog problem in the first place. Once we learn how to handle the leash correctly, the dog is happy--and more comfortable!--to cooperate. Puppies can learn this skill right after they learn to walk on a leash. But it takes us humans longer--took me 10 years!
So now you know the secret! I wish you many miles of happy walks--with occasional right turns, about-turns and other surprises to keep both you and the dog having a great time