They do make "thornproof" which are double to triple thickness on the tread side. These supposedly reduce the number of punctures caused by thorns and goatheads, and maybe thin wires. But the reality is that unless you have a problem, flats are caused by stuff you ride over. And there's not much you can do about that.
Besides thornproof tubes you can use liquid sealants like Slime, or devices like Mr. Tuffy (which I hate), or buy tires with kevlar belts.
OTOH- I suspect that active urban cyclists get flats on average once every 1,000 miles or so (figure from thin air, but probably not a mile off) so getting a flat or slow leak after 400 miles isn't cause for panic.
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