Sorry if this is a repeat to an older thread, but I couldn't find anything. I've had cats most of my life but this new behavior is concerning me. My niece and her 70lb dog moved in with my three cats and me about 8 weeks ago. One of the cats, Sheldon, has not adjusted well at all. He went from only going after the dog when she got near him to actively seeking her out to attack...and within the past 3-4 days he has started going after my niece's feet/ankles when she walks by. He hisses and spits and makes all kinds of noise. I understand why he's doing it (stress and anxiety) but what I need to figure out is how to get him to stop. He has never been an agressive cat until this point (almost 6 years old and neutered). When Meghan is just sitting he'll come over and want to be petted but when she goes on the move look out! The dog cannot even fart without him flying off the handle. Any suggestions? I feel bad for him because his home has been invaded, but no one is going anywhere in the near future.