wow that is amazing im speechless i dont use kong i use the everlasting treat ball products in a medium gatsby can get the small in his mouth but not back out
 Everlasting Treat Ball : Combination Treat Ball & Dog Toy at Drs. Foster and Smith
i have also heard of a toy called gonuts that has two layers a red and a green the green on top if the red ever shows they send you a new one free of charge 
GoughNut .75 
the small one is ten to 20 pounds but for our heavy chewers it might be fine