If the dog understands the no command it will help along with drop/out/etc. If there is something in his mouth then he needs to know to let go. You can try by baiting him with "safe" things at home in the yard etc.Keep a regular collar and a short lead on him while doing this.
When he goes for lets say a cracker on the ground. You should be watching closely make a noise to side track him and make the situation less pleasant while taking the collar and redirecting him to another location away from the troublesome area. This is to help stop the behavior from happening. You should alternate with different "baits". T Never scream it's not that effective anyways

. You can say No! or AH AH AH sahke a bottle filled with coins OR SOMETHING OF THE LIKE. Once he starts avoiding it on the verbal correction be sure to give the dog lots of praise or play time. To let em knw this is the right choice.
After he gets better then switch to a longer lead until voice is all that is needed.
Also the drop it command will be necessary for the times you cannot stop him from the get go. Every command needs to be clear and evident of what you are asking. If the dog hears the command and does not respond within 5 to 10 seconds then they did not listen correctly. And this should not be rewarded. instead give a firm "No" and resart until you get the desired behavior. follow with praise or play
If a dog understands that they can perform a task sloppy and recieve an award then that only encourages the bad habits. I hope this helps
