A chewing question

Question
My black lab, Shaka, is a 10 year old male.  He was neutered as a puppy.  He was crate trained and later (at about age 5 gradually became more difficult to get to go into the crate until he simply stopped).  No problem, I have a large backyard and he has the run of it.  In the morning he eats breakfast and can't get out there fast enough.  Literally, since Friday, April 22, he began to chew the 4 ft. wooden fence until he chewed a hole in it big enough to escape (he goes to my neighbors house and she keeps him until I return home).  I  fixed the fence by putting up new slats and let him out.  I happened to look up and saw him working so hard to get out, he knocked down both new slats and began to force his body through his new hole but not before almost removing his due claw, stepping on a nail and causing himself to bleed from his mouth.  I can't let him out alone anymore until I can prevent him from escaping, eating so much wood and injuring himself.  Could ALL of this be simply boredom after 10 years?

Answer
No obvious answer.  For most behavior problems with an older dog the first step is a vet check.  

Even neutered dogs may be distracted by a female in season, but if that was it, I wouldn't think he would stay at the neighbors'.  

Has anything else changed?