Digging is a hard problem to solve because like wagging the tail or hydrant-sniffing, it's normal canine behavior. Except for the more sedentary companion breeds, most small dogs were bred to hunt vermin, and those critters lived underground. When your little terrier unearths your tulip bulbs, he is probably hot on the trail of a chipmunk or fieldmouse. If your dog is digging to cool himself off in a nice comfy hole, it's too hot for him to be outside in the first place.

If you want to indulge your dog's compulsion to dig, you can always give him a dig-safe area in the yard where you can bury his stuff to keep him away from the garden. If you want his company while you're outside planting those flowers, you may need to confine him to an exercise pen with some chew toys to get your work done.