Q: How do I keep dogs from digging or laying in my flower beds?
You might also create a "doggy digging area" somewhere else in the yard. Make a "dog garden" of soft, easily-dug dirt in a shady area and the dogs may prefer to dig there than in your garden (you might trying "lacing" the area with doggy treats to entice them there to begin with, and then keep the supply going).
There are many products that claim to repel dogs from an area, but I don't know how effective they are. I've heard reports both ways, but you can give them a try to see if it works for you.
If none of this works, you will probably end up having to fence off the area.