Wife and I have always had a Doby since we got married... 5 total. 2 Black & Tan, 2 Reds, 1 White. Every one has been loving, loyal & playful (to a fault at times). We had trouble with the White. He was almost fully grown, not quite a year old. He nipped (and I do mean nip) this stupid neighbor chick of ours on the bellybutton when she walked into our house uninvited. Not a bite, no blood... as a matter of fact it looked like a scratch and didn't break the skin. This dog had an overly playful attitude and to him that "nip" was all play. He did the same thing to us, he'd run up, get ahold of your pants or whatever, then tear around the house running from you. SHE happened to be wearing a set of daisy dukes, so I'm certain wasn't going for skin and likely got some in the process. So anyway, stupid chick goes running off to the emergency room as though it was some major catastrophy, and the dog had to be quarantined at the local SPCA for 10 days. When he came home (with a clean report card) he would get very pissed off if you grabbed his collar....something he'd never done before. I called the moronic SPCA and sure enough, due to his size and an unfounded fear of the breed they had been using one of those stick-ropes on him to move him around. Eventually he bit my kid (9) on the arm as my kid was trying to pull him around by the collar, and that was the end of the dog, unfortunately (and due to some real idiots at the SPCA).
Point is.... treat a dog like crap and you shouldn't be suprised if he/she turns on you.
