Parenting as talking to a brick wall?

I think that the more conscious you are as a parent, the more frustrating situations become when you can just see that things aren’t working, your standard tricks aren’t fixing the problem and it’s all devolving and degrading before your eyes. For me, there’s no situation that pushes me over the edge more than when my kids just plain aren’t listening, but it’s remarkable to me how often talking to your children is eerily akin to standing in an empty field talking to the daffodils.
Our metaphor for this is whether the children have their feet on the ground or not: when they’re really present, really listening and engaged in you, eye contact, leaning forward, wanting to know what you have to say, then their feet are firmly on the ground. The flip side of this is when our kids are out floating in space, far above the clouds, and certainly not in the same room you’re in.
Adults can space out too, of course (especially in boring meetings or in classroom settings), but children seem to be much more prone to this behavior than adults are, in my experience. This is a good thing in my opinion, actually, because “spacing out” is also where creativity comes from, and it’s the inability to pull your feet off the ground that makes so many adults so darn boring. But…

As we’ve moved closer to summer and the weather’s become warmer, we’ve been playing outside more often, and sunset is later and later, our kids seem to have jumped into their spaceships and are flying out there a la Spaceman Spiff from Calvin & Hobbes.
Which, I suppose, isn’t a huge problem.
Except when I’m trying to talk to the kids, in which case I want a tractor beam, a grappling hook, some way to at least temporarily bring the little astronauts back to the launch pad for just a few minutes. But darned if I haven’t yet figured out this magic technique!
The other day was a classic example: my 5yo son G- was standing on a chair in my office, looking through my tchotchkas from trade shows, and he picked up a flashing lapel pin from Google and went to put it in his pocket. I stood next to him and here’s how the dialog went:
me: Honey, I already gave you one. You can’t have that one. Please put it back.
he: no reaction
me: You can’t have that, please put it down.
he: no reaction
me: Look, you have one. I’ll help you go find it if you want.
he: no reaction, keeps moving pin towards his pocket
me: This isn’t working. You need to put it down because it’s mine. You have one, and I’ll help you find it.
he: starts to sulk, still hasn’t put pin down
me: G-, put it down now. It’s not for you, and I’m sorry you’re getting upset, but it’s not for you. Not everything I own is yours, some things are for Daddy.
he: starts to slump. Clasps pin in hand
me: (voice rising) I’ll pull it out of your hand if I need to. I don’t want to. Please put the pin back right now.
he: no reaction
me: Shall I count to three?
he: no reaction (of course)
me: one…. two….
he: fine! (puts pin down reluctantly, walks out of office quite upset, collapses half-way up the stairs in tears)
me: (feeling terrible, darn frustrated that things have played out as they have) Let’s go try and find your pin, shall we?
he: (cries)
And so it goes.
But this kind of situation just drives me bonkers. What could I do that would change the dynamic of the situation? Talking is just making noise, but with a 5yo who is deep in the acquisition phase, it’s just about a daily occurance that he finds something that he can’t have, and giving him lots of little “treasures” doesn’t affect the frequency of this occurence.
Thoughts? Suggestions?
Fortunately, kids bounce back really fast and within about two minutes G- was up, out, and skateboarding in the front drive, happy as the proverbial clam.