Thrift store electronics- buy some, take them apart with screwdriver.
Hammer golf tees as nails into cardboard boxes.
Boxing gloves for punching trees.
Any ideas or things you've done to allow this phase to play out with less trouble?
What is he drawn to? And what do you think is behind it? "destructive" feels like quite a broad term.
Is he doing it out of anger, or curiosity, or kind of a need to interact with his stuff in his own way, or what?
My son still takes everything apart at age 9. The upside is that he's now pretty good at it, well you would be really. But there is one thing which is that in order to take stuff apart, electronics and so on, to see how they work, you do have to be pretty careful.
How about sandcastles, or mud castles or whatever? Do you live near a beach?
We had lots of fun with this when my son was little. There was all kind of strange stuff in the freezer for awhile. Chisel and hammer soon gave way to dremmel and drill, though... We also had a couple big chunks of limestone that were fun to chisel, and wood to whittle.
My son has always loved taking stuff apart too, and has dismantled everything from the Ikea furniture (as a toddler) to toasters and old computers. We found lots of electronics in free piles and garage sales.
How old is your son? Mine used to like doing our paper shredding for us when he was younger. Water balloons were fun for quite awhile. And we had a big sandbox for building and destroying entire worlds ;)
I think there is reason to be concerned and to do something to redirect these urges. It sounds like you've done the radical unschooling thing so far: looked for value in what he's doing, even when it's not stuff that's typically valued, and supported him in pursuing what he seems to enjoy. I think you've been very open-minded and creative. I do however wonder -- as do you, it seems -- whether some different tactics might be helpful.
I do wonder if the more basic urge -- to feel powerful, I assume? -- could be satisfied in ways that don't veer so close to aggression. I think it's a lot to ask that a young child be encouraged to act out the urge to be powerful against [designated] objects by hitting and breaking them when he's not angry, but to use entirely different strategies when he is angry. I would not want "hitting and breaking things" to become the default coping mechanism for pent-up energy, anxiety and feelings of powerlessness. It veers too close to aggression for me, and is too likely to be overgeneralized (to people and valuables) by a young child.
Like you I also have a problem with the waste and disrespect of breaking things. We've had "destruction fairs" with electronics in the past, to feed my kids' desires to learn how things are put together and how they work. But that was a special thing we did with carefully chosen objects that were destined for the recycling heap, we tried to separate out recyclable components from the rest, and we also did a fair bit of creating along with our destroying, using salvaged bits to create sculptures like miniature electronic "insects", and trying to fix mechanisms where possible (the most fun was a 1980's clock radio with the rolodex-style wafers of numbers for the time). So I've tried to redirect the delight in taking things apart into environmental and creative impulses. And our rule has always been to only do this with things that are truly garbage and cannot have value added to them otherwise: not just with things you don't like any more, or things that were inexpensive. And of course you always ask first, and get appropriate guidance about safety -- this is what a capacitor looks like, this is why it can give you a nasty shock, this is how to pry things apart safely eg..
I wonder if you could look towards physical achievements and exercise rather than destruction to give him that sense of power when he seems to be craving it. Running around the outside of the house, riding a bike up a big hill, bouncing on a trampoline, swinging on a doorway chin-up bar. "Show me how fast you can go!" or "Let's see how high you can bounce/swing/whatever!" That sort of thing. Encourage physical exercise and feats of strength to become his default way of expressing power.
And of course all the little things in his life that you can possibly give him autonomy over (whether to clean up his room, whether to finish his lunch, what, if anything, to wear on his feet, whether to go for a walk or not, that sort of stuff) will probably help feed his need for power and control over his own life.
Just some meandering thoughts.
Oh, we do this too! And I thought we were the only ones with a living room decorated with sculptures made from broken remote control airplanes and old circuit boards!
Mama Amie, my son dug an ENORMOUS hole in the yard when he was that age... he and a friend were determined to link their houses with an underground tunnel. His friend's mom said it was fine for the tunnel to lead to her yard as long as they started digging at our end ;)
I think that some young kids have a real need to feel more powerful and more independent, and a ton of physical energy that can be hard (for them, I mean) to know what to do with. I like Miranda's suggestions in the physical realm. Is your son competitive? At that age, some kids seem desperate to be the fastest, strongest etc and finding a safe outlet for that might help.
Maybe something he hasn't done since he was a tiny (blocks and planks and that stuff). New skills that require more work and time, something he hasn't already associated with demolishing. (Yet.) Perhaps learning to piece things back together again, like a "real life puzzle". Ballpoint pens are a start. Take them apart and see if he can't figure out how they go together to make them "click". Too easy? Get a thrift store bike, take it apart and try putting it back together again. Just ideas.
This reminds me of how my ds used to like to build sturdy constructions with blocks and then see how well they'd withstand having the wood ball from a pounding toy bowled into them. We'd see how many rolls of the ball it would take to knock it down, with the goal being to make something that was hard to destroy. Sometimes we'd each build a tower. Then when we were done, we'd take turns bowling the ball into the other person's block tower.
Ah! Yes! Refined destruction!
There are those "classic" challenges, like building a contraption to protect an egg getting thrown off a roof. So, not piñata-style free-for-alls, but a certain, controlled force like that bowling ball.
And speaking of bowling..... that might be something fun for someone who likes to knock things down. Destruction combined with finesse.