I had lab a number of years back that had a very hard mouth. Put the dummie away if the dog is going to be aggressive with it. Cut a 2×2 or 2×4 depending on the dogs strength. Then pound nails throught the 2×2 or 2×4 so that the sharp ends of the nails are what the dog has his mouth on. This worked very well for me with that dog, but I had another that it didn’t work for. With him I had to retrain him on the hold and fetch command. A very easy way to do this is clear off a spot on your workbench or somewhere where you can get the dog off the gound. You will need a place where you can attach the dogs collar to something solid so he can’t move. You first start out by having the dog sit, you then place two fingers in the dogs mouth and give him the hold command. If he spits them out, you grab his ear and rub your thumb nail on the inside of the ear for a few seconds. Then repeat this, place your fingers in his mouth and give the hold command agian. As time passes the dog figures out that if he drops/ or spits out your fingers out, his ear is going to hurt. If you can get the dog to hold you finers in his mouth for 15 secounds give hime the drop command, and praise him…a lot. Once you master the fingers, move on to something else, a piece of wood, a hammer, it really doesn’t matter what you put in his mouth, just not the dummie yet. As the dog masters this, you should be able to put anything in his mouth and he will hold it until you give him the command to drop or give.At this point you should start to do this with the dummie, make him hold it for 15 seconds, give him the command to drop or give, and praise him. The praise is a must in order to make this work. If you have the dog holding the dummie and he starts to mouth or chew the dummie, you just grab his ear and give hime the hold command,if the chewing continues, rub you thumb nail in the inside of his ear until he holds, wait 15 seconds, give him the drop or give command, again lots of praise when the dog does it right.I know this is force training, and not always the best way to do things but for a dog that is bull headed this worked great for me….goood luck with the hound