I have two huskies, Logan and Buster. We just got a new toy last night to try a toy with a squeaker in it. We only wanted to get one to see if they liked it. We won't be getting a second until we get back from a short vacation. Usually, we let them play with two racquetballs so they each have their "own" toy.
Well, long story short, we wanted to see how well they would play together with one toy. Buster plays well, if he gets it, he will romp around, throw it, squeak it, slap it, etc for a few secs, then bring it back if I am playing with them. Logan, however, when he gets it, he will take it straight to his crate or will just stand over it with his head down. I thought they were just playing at first, but then Logan bared his teeth and growled. I tried the cesar milan thing, which usually works, but then I had to snatch him up by the collar. I want them to learn to play together.
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Update, since then, he has been bringing the ball back, but still does the head down, ears back sometimes. I'm just trying to correct him and tell him guarding is not ok.