I own a dog which was just like that, frustrated me, no doubt....However, she's pretty much completely over that now at 20 months...probably has been for 6-8 months....once in a while if she makes a great snare on the tennis ball, she might take one victory lap around my garden before she returns it to me.
I'll have to give you quite the high praise for being patient..waiting a half an hour...that's out of my league.
Rewinding the tape, I know I brought the game of retrieve where my odds were better, so we played indoors in a confined area...it took awhile but she started giving it up close to me.
I also recall and this is more to your point....I read up on this attitude called "right of ownership" exhibited by dogs ( humans as well I suppose )...it was an education for me and turned the tide regarding my dog getting all possessive over certain objects....tennis balls, frisbee and sticks etc.
What I have now come to find as a benefit of this puppy behavior is the usefulness of these items ( frisbee in my case ) as a training "treat". There is a video posted by Baliff showing this type of treat being used...great video.
Anyway, I am getting ahead of the current situation..... my reading up on right of ownership by a dog opened my eyes. Body posture, where they place the items they are possessive of and how they let other dogs and humans know "this is mine" ....understanding this helped me curb the situation you are experiencing.
Wow !! waiting a half an hour....that is patience !!!