I didn't make this up myself I read it somewhere and tried it... Does you dog dig holes? Place in the hole one of their own bowel movements, fill the hole back up with soil and tamp it down. This will eliminate them from digging in this spot again. Not to say they won't dig anymore holes, but they won't keep digging in this spot "making their way to China or the USA". Doggie holes can be down right dangerous if you aren't expecting one in the lawn.
An interesting use of a dog's olfactory nerves. Now it's a good place to put a plant, fido does not want to dig there anymore. Jerry
Sorry, Philip, I have no remedies for cat digging issues. Um...it makes good fertilizer for the flowers, though. nor are they as prone to digging a hole bigger than themselves. You should be safe. I know my cats haven't dug anything of significant size, it is just disgusting when I find it in the garden ...usually with my hand trowel.