I guess this might not be the most popular answer, but I say next time the dog bites or even mouths you, get ahold if the scruff of its neck, give it a shake, and growl just like his momma would do. It takes them by surprise and they don't like it, and they learn to stop...hopefully. But just don't let anybody see ya doin' it cause they might think you are a little off upstairs
. Or you could try a spray bottle mixed 1 part vinegar to 3 parts water and spray the dog right in the nose (not the eyes) when it bites along with a stern, "No bites." That should work, too. You want the dog to be totally alarmed when it bites. Not totally freaked out or scared of you, but you want them to decide they want nothing to do with the response they get from biting, to the point that they stop biting.You will get it, a dog that age is still probaby just feeling out the way life is going to be, so you just have to show them how it is going to be. Good luck. My male dog was the worst about this as a young puppy, but now he wouldn't bite you probably for anything. Now it's different with squirrels