In article t8mYj.1241$ay2.1029@trndny01,
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?
Liz

I'll vote with those who actually know what a carriage bolt is, and
second the suggestion to grind a screwdriver slot in the heads with a
dremel.

The nut=splitter is not a bad idea, either, if you have access to use
it. Picnic tables are sometimes constructed with counterbores for the
nut, so you'd not have access for a splitter.