harley: the trainer I recently took my rescued dog to said that dogs dig because they are bored. They should be exercised, which will help stop the digging. My newest is a digger but, to his credit, he digs for ground squirrels and chipmunks, so I can't fault him too badly.
I don't think the shock collar will work unless you are there to see it and activate it when he digs. Filling the hole with his poop might not stop him from digging either, unless the dog gets brewer's yeast and garlic, which makes their poop unsavory to them (that's the stuff that keeps dogs from eating their own or other dog's stuff).
One thing that worked with one of my other dogs was a medium sized plastic soda bottle with a couple of coins in it. It rattles and makes a noticeable noise, and you can throw it at the dog to distract them without hurting them in any way. That has worked on four of my dogs and although I have not had to use it on my newest, all I have to do is (in plain sight) drop a couple of pennies or dimes into a soda bottle and cap it, then shake it a few times, and my older ones sit right down and look like angels who didn't do nutin. But, you have to catch the dog in the act. You can't punish them after they have stopped whatever they were doing and have come over to you - if you punish them then, you punish them for doing what you wanted them to do - it sends the wrong message.
You gotta ambush them while they are at it. Wap 'em once with the soda bottle and they will (or should) react like they have been bit. Point to the damage and tell them 'No', in a firm voice. If they go back at it, wap'em again and continue with the program until they stop. I does work. HTH. Mikey.