My girls Sadie & Maddox like to eat dirt. They find a really good patch of dark, organic, earthy goodness and bite right into the ground... it's pretty funny to watch. Their bowels are now part of the geologic process, pooping out little rocks.
The trouble is... I don't want holes in my lawn. I got this idea from my Aunt Betty when she lived out in Sequim, Washington. If your dogs have an insatiable urge to dig that can't be trained away, the next best thing is to give them an appropriate spot to sink their claws. Make it neatly edged, loaded with a mix of clean pool sand and yummy dirty organic topsoil, and be mindful (if it's near the fence, like mine) that they can't tunnel underneath. Throw in a few fun finds (Kongs, bones, etc) for your inquisitive friends to unearth. Every time they start to dig in an undesirable place (like under the barbecue), redirect them to the digging box and praise them when they start to dig there.
Mine is a simple 3x5' box made with pressure treated wood. (If your dogs chew on wood, you may opt for a non-PT option.)
The digging box sits at the edge of my yard, in the semi-circle of mulch designed for the dog agility equipment & other play things.
Happy girls going to town in their new digging box!