he is pretty hard on the canvas dummies, occasionaly puncturing them with his teeth. the two things i can think of that has made him hard mouthed is he was a year old when i got him and i think the last owners let him play with plastic bottles and the other thing was the dummies i initialy trained him with was the hard rubber dummies from the launcher, i think they were so slippy he had to bite down on them hard to keep hold.