The ghost coon is hiding in a hollow fence post.
The ghost coon gets its name from the fact that it seems like whenever it gets treed it disappears into nowhere. Billy makes a bet with the Pritchards that Little Ann and Old Dan can get the ghost coon. They do find its scent and tree it, but then they lose it. He pays up, sad that he lost the bet. Then Little Ann indicates that she knows where the coon is, and they find it hiding in a hollow fence post.
Old Dan, not understanding why Little Ann was bawling, stood and looked. He walked over to the post, reared up on it, and sniffed. Then, raising his head, he shook the dead leaves in the bur oak tree with his deep voice. (ch 13, p. 124)
Billy is very proud of his two dogs. In this case, they were just about to give up when Little Ann figured it out. Old Dan confirmed her find, and the boys were able to get the raccoon out of the post.