I use the "Leave it" command for these type of issues. I call "leave it" anything I don't want in my dogs mouth. I begin with the dog on the leash and a dry biscuit. I toss the biscuit just out of reach and when the dog goes for it I give him the command (I usually have a little more urgency in my voice). When the dog looks to me I instantly reward with a separate meaty treat. I do that about 3-4 times, until the dog no longer has interest in the dry biscuit. At that point I up the level of difficultly by adding something more interesting than a dry biscuit (a steak, shoe, dead animal, etc.). I go through the same process. Once he's no longer focusing on the "Leave it" item I put it in motion. I walk the dog all around it, over it, and even pick it up and drop it right in front of him. If the dog goes for it I cover the item with my foot so he can't get it and give him the command. If he leaves it like I want I'll give him a treat if not I just move him away so he can't get it. After about 3-4 days of this with a treat reward the dog becomes pretty reliable to the command. At that point I always give him praise. I call it my life saving command because you never know when you'll need it. I've called my boys off of skunks, other dogs, food, you name it.