How often can I give Lucy marrow bones? I picked up a package at the pet store today to help clean off her teeth (the vet wants $500 for a teeth cleaning...eep! I'll do it, but not before trying other avenues!) She's going to town on that thing, scraping like crazy, so it seems to be working--but how often should I do this? Once a week? When I notice it getting bad? As a special treat? And do I take it away at a certain point?