Have you had Duke, your 5 month old male rotti/shepherd mix -- neutered? Vets are neutering/spaying dogs much earlier than they used to.
I gather that you're giving both dogs equal amounts of attention around the house, etc. This could very well be a phase that Duke is going through. The best thing to do is to ignore it. It's tough to do but in the long run, everyone will feel better.
© Nancy Kitching 2003
Dog Trainer Member of CAPPT, CKC, OKC (Ottawa Kennel Club), and Bytown Obedience Club in Ottawa.
Hudson, Quebec J0P 1H0