Dogs love to dig. Training your dog will keep him off the garden.

I rescue mostly chihuahuas. Adopt, adopt, adopt!!!!

it's not easy at all but u have to try

About punishing, it's really no good - it'll only make your dog scared and he will not relate it to the wrong thing he just did. Screaming also won't work, most dogs see their humans as the 'alpha' in their pack, and when you start yelling at them the only thing they understand is something like "our leader has lost it, who will protect us now?". You have to keep an eye on her, stay around and disencourage her on digging the garden. When she starts, say a firm "no" and, if you want to, you can spray a litte water on her face (just a little!) in the exact time she's doing something wrong, always saying NO right before you do this (later she'll relate the NO word to bad things, and will stop, even with no splash of water), and distract her with toys or snacks when she stops digging to positively re-enforce her.