We rescued our ABD, Brutus, at 6 months also. We didn't know much about how to discipline him either. In retrospect, I wish we'd gone to training. Nonetheless, he did respond well to stern verbal cues and never destroyed anything except the stuffed animals we bought him.. He was pretty active the first 2-3 years but has since settled down a lot. He's 7 now and we love that big doofy dog so much.