I use an e-collar to break them from digging. Set on a high shock. No voice command - at all. You want them to think the shock came from the hole they are digging. Ideally, you also shouldn't be visible. The shock has to come as they are actively digging, not at any other time. At no point do you want the dog to think you shocked them. It's pretty aggressive so I don't use this method until they are well settled, at least a year old. Basically, the same process we use for snake avoidance training. Take your time and be patient. Make sure you are set up correctly or you won't like the results.