I’ve heard several different methods for slowing a gobbler down. One was to clamp visegrip to the middle of the leg quarter so he has to gnaw around it. Another is to use cable ties to fasten the leg quarter to a metal tube, like a vacuum hose extension. My dogs don’t get chicken due to allergies, but they eat turkey and when I give them a piece of turkey they usually crunch along the length of the bone several times then sort of inhale it. Basically, they break up the bone before they start actually eating, then they eat fast. Your dog will be fine, just keep working at the chewing thing. He will learn.
