SA dogs are tough. I used to have boxers, which are famous for this problem. I agree with getting medication from your vet to help, but increased exercise and mental exercise are also crucial. One walk a day for a mile isn't enough for this type of dog, IMHO. I would try 2-3 walks a day at 2-3 miles each (gradually work your way up to this level, so as not to injure your dog). Mental exercises will wear them out, as well. Google Brain Games for Dogs or Mental exercises for Dogs to get ideas. You may also want to consider enrolling your dog in agility class. Many dogs enjoy it, and it engages their brains as well as giving them (and you!) physical exercise.