Liz Megerle wrote:

I built a picnic table several years ago. It took a hit from the snow
plow this winter. It's worth repairing, but I can't undo the carriage
bolts. The square part of the bolt head strips the wood when I put a
socket on the nut. Next weekend I'll try pounding a screwdriver under
the head parallel to the surface of the wood to engage a flat side of
the square. What do you experts do?

I'm in the Dremel/anglegrinder camp- cut/grind the nut off & drive out
the bolt.

But if I was really reaching for a good excuse to buy a wire-feed mig
welder [or knew someone with one] I might try tack welding a nut on
top of the carriage bolt. Weld inside the nut - don't overheat.

Jim