This wasn't too much of an issue when he was a puppy because you could physically restrain him. But now he's an adult, his low center of gravity and stocky build means he can easily tow you along behind, putting not just him, but you in danger. Now you find yourself getting tense on walks, in anticipation of having to shout at the dog to make him take notice.
The other day things got so bad, a passer-by became involved and scathingly asked if your dog knew how to sit or not. This hurt at the time, but later you realized it was a perfectly valid question. If you could get the dog to sit, this would rein in his impulsiveness and get him focusing. All of which sounds simple enough, but how to make it happen?
Although a simple action, this gives you immediate control over the dog as it keeps him in one place. This can mean the difference between him running out onto the road or staying safe at your side.
The 'sit' command is not difficult to teach, but does require patience and repetition. Keep your training sessions short, but repeat them throughout the day. Any training should always be fun, so be lavish with praise and keep your voice excited and happy. Be sure to encourage the dog by rewarding his success, and if he doesn't do so well, don't worry, there's always next time.