This is not exactly about pets and shells - but about animals and shells
anyway.  A friend in British Columbia (western Canada) tells me he used to
clean shells in the back yard, and let them dry on the picnic table.  But
now he does all his cleaning indoors because bears were coming and taking
the shells away, or just crunching them up and leaving them there. And you
thought cats and puppies were a problem!

Paul M.