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.

We had a resource guarding issue when Ripley first came to us, it was mainly with bones. What worked for us:
Give him the toy in an open space so that he cannot hide, and when he has it sit close to him. If he is fine and not growling then praise him. Thats when you start to move closer and closer until you can remove it without him growling. We continually praised if she was accepting us being close and having our hands close until now we can remove bones with very little effort. It took us a few weeks of this method so keep at it.
We also used our cat as a help. We made him walk past her a few times and she finally started to relax and when she did we praised. Its about desensitising and making them confortable. Now she rarely growls and then usually its when Tika sneaks up and tries to steal it, but its always a hey thats mine growl and nothing menacing or aggressive.

Hope this helped.