This has been an interesting thread to read, and while I do not have any suggestions on nail chewing, I can say I am alarmed at how many owners have difficulty trimming their dogs nails. I have seen many of these replies stating their dogs nails are only cut once or twice a month, and many of the pictures posted show dogs with far too long of nails. I have owned RRs for over ten years, and am on our fourth, all of which have had no problem getting their nails worked on. My current RR is 15 mo. and has her nails trimmed weekly (that is after 35+ miles of tarmac running while training for marathons). I am able to handle this alone, and she calmly sits while I work with her feet.
I have found the best method for establishing a nail routine is to make known to the dog who is in control. I flip mine on her back, pull all four feet together, sit on the floor with her head under one knee, and wrap my legs around hers. My earlier three RRs were introduced to the Dremel very early, however our most recent addition is a rescue, coming to us at 6 mo. Establishing a proper nail routine can be done at any age, and is imperative to a RRs overall health.
Short nails lead to less foot problems, and hopefully aid in eliminating the persistent nail chewing.