Hello all, Just to give everyone a little backstory, my wife and I are current owners of a neutered three year old chocolate and tan male (Toby) who we've had since he was a puppy. Toby is fairly well behaved with the occasional stubborn moments, but he has not been heavily socialized with other dogs throughout his life. In the past, we had good experiences introducing him to my wife's grandparents' elderly female whom he got along well with, but he's shown signs of being timid and insecure around my in-laws' mini pin and dachshund whom he's been around on multiple occasions. Well I decided to 'complicate' our life a bit by recently bringing home a female shaded cream puppy to add to our family. As with most of my decisions, I researched and over analyzed the repercussions of this decision, but felt confident that despite Toby's initial reservations, he would likely embrace and accept this new female dachshund pup over time. Unfortunately, much to our surprise, our initial attempts at introducing him to our new puppy did not go over well AT ALL. Our initial attempt was a meet and greet in the yard, only to have him continuously growl/bark as if embracing some predatory instinct. After that failure, we tried letting him sniff her indoors with the puppy cradled in my wife's arms and me holding Toby, only for him to continue with the same nervous growl and nip at the puppy's head unprovoked. Since then, anytime he is near her, this tends to be his typical response of nervous growling or barking, especially if my wife or I are with her. Well I recently set up the puppy in our office with a baby gate restricting her access to the rest of our home, in the hopes that after a week or two, Toby will eventually grow accustomed to her scent and her constantly being present. My issue is, although we understand there will be growing pains as our new pup fully integrates into the family, it does not appear that Toby is making any significant progress towards acceptance of her and has shown continuous signs of jealousy/aggression. Currently, he cannot be trusted even remotely near her without fear he'll begin to act aggressive and possibly cause harm to her. Aside from the typical "rehome the puppy" response (which we are willing to do should that time come), I'd like any advice or any other methods that may help in resolving this matter.