My females do it after going #2
My trainer says it is away of marking "their" turf and I should discourage it by getting them to move away from the site a bit while I pick it up
Muffin does the same thing after she goes poo, and my ol gal Luna does it to LOL!! And yes it is a way to mark turff, they do have scent glands on there paws.
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A rescue is never to old to learn to be a real dog.