There are a few techniques that I have used with a lot of success. One is to lay chicken wire in an area where there is constant digging. This way, when he scratches his feet on it, he gets negative reinforcement. You can't chicken wire your whole yard, but you can do the flower beds and other favorite places where they dig.
I found a great article for you, too:
How to stop digging
If you do some work in the garden, roll out the hose and fit a sprinkler on the end. When the dog goes to investigate the area, turn on the sprinkler. In this way the sprinkler is telling the dog off, and not you. The added bonus of letting the sprinkler do the work for you is that many dogs will learn not to dig whilst you are present but can dig away happily when you are away from home. The sprinkler causes the dog to think that the actual garden is chastising him and does not realise that you were involved at the tap end!
What if you do not have a sprinkler, or the dog is digging at a point too far away for the hoses to reach? Treat yourself to a toy water pistol. For very little cost, you can buy a water pistol that has a good accuracy over several meters. Then you just hang around in the garden and wait for the dog to start digging. As soon as this happens, deliver a jet of water at the dog, aiming for its head. Say nothing; act as if you were not involved. This can have a similar effect to turning on the sprinkler.
If your dog seems hyperactive, chews destructively and digs holes then this could be boredom. Take the dog out away from the garden for exercise for at least one hour each day. Play games of fetch with a ball and do not restrict the dog to the garden - allow him into the house. The more the dog is alone the more likely it is to dig. Leaving toys stuffed with food and goodies when he is left alone will make the "home alone" times more stimulating.
Dogs that dig at fences may well be bored and trying to get out to something on the other side of the fence. The scent hounds will especially do this when they can smell something really interesting on the other side of the fence - so watch out if you have a Beagle. If there are any gaps in your fencing fill them in but also watch for gaps below the fence - fill this in with concrete or attach chicken wire to the bottom of the fence and curve onto the ground, burying it below the surface. For dogs that do keep going back to the same hole to dig, try lifting some of the dog's own poo and placing that in the hole - few dogs will dig through their own feces.
If you find that despite all your attempts to stop it your dog keeps on digging, then you might consider ceding a portion of the garden. If your toddler likes to dig, we buy them a sandpit. The same can apply to the dog. Provide a sandbox - or just a small corner of bare, dug over earth, and bury bones and favourite toys. At first, leave part of the toy sticking out of the ground, take the dog over to the area, and act excited as if you are about to discover lost treasure. Let the dog dig to get the toy and praise like mad.
Whenever you then see the dog digging in other parts of the garden, switch into your "excited - buried treasure" routine and encourage the dog over to the digging area. Better to have one small area dug up by the dog than to have your whole garden looking like a minefield.
If you feel your dog is digging because he is bored and you decide to obtain another dog to keep him company, then expect to have two digging machines! Far better to solve the first dog's digging problem before multiplying this by two.
source (with permission)
Let me know if you still have questions or if I can help more!