Objects such as a can of pebbles rarely works long term because people don't go around carrying a can of pebbles with them so the behavior is never reinforced.
It would be hard to say why the dog does this but what should be done is the dog is taught a leave it command to 100% firm. This means practicing with a variety of objects so the dog learns leave it means to leave everything it has it's mind on and await the next command,
Having your husband train the dog will help as well. All adults in the home should be involved in training.
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.
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
For more videos of clicker training other commands go to google search and type in “clicker training videos”
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
clicker leave it https://www.youtube.com/watch?v=zNAOe1djDyc
clicker maintaining focus http://www.clickertraining.com/files/auto-eye-contact.pdf