Herb Gardens and Pets

I'm wondering if you can help me with something. My animals (dogs and cats) have the bad habit of digging in my outdoor herb gardens every year. Is there anything you know of I can plant or do that will deter them from this? Maybe there's something with a smell that drives them away?

Unfortunately there are no plants that we know of that reliably deter cats and dogs. Rue (Ruta graveolens) is said to repel cats, but we have not confirmed that, and, in fact, we are doubtful that it would work. We have a joke here at Richters that a better strategy for controlling cats is to scatter catnip seeds over the neighbours fence – but that would be most unneighbourly!
Part of the problem is that most herbs do not release chemicals to the environment (such as essential oils) unless the plants are touched. Even catnip escapes detection by many cats unless the plant is bruised. So even if there are plants that cats or dogs dislike, they are not likely to work reliably even under the best of circumstances.