Keith's biggest fish was a 70-pounder. My girlfriend made a tub of coleslaw and 40 pounds of hush puppies. Musta been 80 people over at my house. End of the night, there wasn't a single bite of fish left over. Nothing on earth eats like a fresh flathead.
Cypress lasts the longest, but no box lasts more than about three years.
The tremendous load of sand and dirt in the current simply grinds the top of the box off in that time. The river likes to shuffle the boxes. Sometimes it moves a box upstream or downstream from the original hole or log where it was set. Sometimes, it'll bury a box for a year or two, then return it. Sometimes it just spirits them away.