My dog has a muchy grip on the sleeve. Is there anything I can do to fix it?

Question from Brian: I have a 3 year old German Shepherd. He is my first Schutzhund dog and we are trying for our SchH II next weekend. My problem is that my dog has developed a munchy grip on the sleeve. He's not biting hard or pulling on the sleeve, he just bites and readjusts over and over again. He's a very good dog, lots of courage and strong in defense. I'm not certain what has created this or how to fix it or even if it can be fixed.

Here is a little background information. We do not have a great deal of experience or have a regular helper in our club, therefore some of the bite work has been less than desirable. In terms of presentation, on the sleeve and reading the dog, I'm the most experienced with doing helper work, which is not very experienced. So, I try and guide the helper while I'm handling my own dog. Unfortunately, sometimes this leads to pressure from both sides. It seems to me that this pressure combined with poor mechanics, lack of knowledge, and a lack of presence by inexperienced people trying to learn the work is deteriorating my dog's grip.

Is there anything that I can do to make his bite more firm and calm? If there is, should I also stop doing protection with inexperienced helpers?