Then you want to give the leave it and heel command and continue walking.
And no, the dog needs to be on a leash. That would be the law. So work on the heel and leave it commands at home first and don't take him out in public until he has learned them
Always start your training in non distracting areas and gradually move to more distracting areas slowly. If at any point you move to a more distracting area and the dog acts out, then you have to go back to the last spot he was listening and train longer there, before moving forward.
Also, always remember as you start moving to more distracting areas, you need to up the ante of reward. So, for non distracting areas you can use soft dog treats broken up to smaller pieces , but when it is more distracting, you need to up that reward to chicken or hot dog slivers.
Also for things like leave it and a recall, you should start on a six foot leash and gradually move to a 30 foot leash as the dog progresses on the commands. This is because the dog needs to know that you can still get him back to you at a distance if it runs off. A 30 foot cotton training lead is very lightweight and the dog forgets it has a leash on, which further proofs dogs in their commands. Start at ten feet , then move to 20 feet then to the end of the 30 feet as the dog progresses.
If you have never used a clicker , you have to load it first before you start training. This just means you do 10 to 15 repetitions of clicking and treating so she knows that after the click sound, she is rewarded. The click sound, as you train, is actually a marker that she has done the right thing. The clicker costs about 2 dollars in a pet store.
Zac George -loading the clicker
Clicker training/positive method training/ print off
use a variety of items for training leave it so the dog knows it pertains to everything in its sight. Include using a remote control car for moving items
the leave it command can be used for barking. lunging, chasing, and anything dangerous dropped on a floor. The remote control car can be driven around the house or yard to represent something in motion that you want the dog to leave alone. Sometimes it is a wild animal or sometimes a real car.
clicker leave it https://www.youtube.com/watch?v=zNAOe1djDyc
clicker maintaining focus http://www.clickertraining.com/files/auto-eye-contact.pdf