Gargoyle, you are absolutely correct. I think I my brain must have switched into "standby". Thanks for setting me straight.

Jon W., I came up empty after searching my resources. However it was not for nothing. I learned that "barking at a knot" is a cowman's way of referring to the impossible.

Some further thought came up with the notion that the " former Cajun Louisiana congressman"'s expression may have been more figurative than it would first appear. If one were a raccoon which had been tree'd by a pack of dogs, one might be said to be between the bark(s) and the tree. That would be a tight situation to be in.