We had one vicious little Dach that ended up sweetening up after having extensive back surgery. He had some complications and a lot of pain. The owners brought him in twice daily for morphine injections. Every time he tried to bite or snap, he got instant correction for it with severe pain! Then he would get his shot and felt better. I think it was a combination of the "punishment", plus realizing that after he saw us he felt better, that finally sweetened him up. Before that, he was one that would take your face off if you weren't VERY careful!