There is not a special disc which will prevent this, make sure your dog has plenty of rest and water while practicing. Bloody tongues are very common and USUALLY not a serious problem. With responsible training and paying attention to your dog’s condition, you stand the best chance to prevent this. When your dogs get tired and hot, they have to expel their heat through their mouths and this causes panting and your dog’s tongue to enlarge. Diligent attention, plenty of breaks to cool down, and using quality discs are the keys to preventing this.