OR put up fencing around your beds

OR remove the dogs from the area.

OR put the dogs on anchored leads in the yard out of reach from the beds.

OR get some device for training them and sit out there waiting for them to dig and then deploy the training device (loud noise, loud verbal commands, water blasts, shock collars).

Dogs can be trained not to do this type of behavior but it takes time and real effort on all parties parts. I recently saw an episode on "it's me or the dog" on animal plantet where the lady trained dogs not to eat their own and the other family dog members pooh. She reinforced them with treats when they obeyed a command to "leave it" which was by using little flags in the yard. She'd place the flags at the pooh site and then command "leave it" when they left it alone, they got a treat. She started out just using the flags other places with the dogs, so that they would understand what they were being trained to "leave" which was the flag association. then it became related to the pooh as well.