strange new behavior

Question
I have the distinct feeling this may be a new one on you...here goes...Sarge 4 yr old Male Greater Swiss Mt Dog.  Some quirks, possessive of yummy treats (growls), doesn't like to share anything (his bed, his space, his ball, his dinner).  Chesney, 7 mos Male Yellow Lab.  We've had Ches for 5 mos.  Up until 2 weeks ago, things between the 2 of them was ok.  Sarge was moderately interested in Chesney, would play daily if he felt like it, seemed to enjoy being out walking our 2 acres with a buddy or laying in the shade together.  Ches seems to love his older brother but wishes he wouldn't growl at him when he walks by in close proximity and relax a little bit.   2 weeks ago, Sarge started acting weird.  Drooling, uncomfortable and anxious to get in the back door from the outside.  Then I noticed that he wouldn't follow me around the yard like he used to but would remain on the sidewalk.  I called him and called and hit my thighs and he wouldn't budge, just stood with his head down wagging his tail, looking at me.  He looked like he wanted to come but couldn't.  I grabbed the leash, always a good thing in my house, and put it on him and walked him down back.  He acted like he was on hot coals and made a bee line for the mulch, having no regard for me on the other end of the leash, he avoided the grass by following the mulch to the dirt to the gravel, then bee lined it to the perimeter fencing and pee'd.   A little further, he pooped.  I left him off the leash and he looked "stuck" again, head low, neck extended, looking right and left, not knowing what to do.  I called to him, nothing.  He started foaming/drooling for about 2 mins then sprinted the same route in reverse all the way to the back door.  I've been "helping" him like this for the past few days.  Last night, I decided to take him a different route-he planted his feet, resisted, eventually gave in but again looked like he was walking hot coals.  Now, for Chesney's part in this...he poops and pees all over the yard, he doesn't have a "special spot".  Sarge has always been a bit regimented in his toileting...follows same pathways, same spots.  Have you ever heard of such a thing?  What's your advice?  Hand walk Chesney and get him to poop and pee in a certain area?  Will Sarge get over this?  My poor husband fenced our entire property so we could just open the back door and the dogs could be free...my fear is that this behavior is just the begining of Sarge's dislike for Chesney and that aggression and nastiness is sure to follow.  So anxious to hear your input!  Thanks for your time, Colleen and Sarge

Answer
By any chance is the new fencing the "invisible" type?  The behavior you describe sounds like he is terrified of something.  Some dogs that are contained in this fencing become scared of the entire back yard.  I can't imagine that the poop is the issue, but stranger things have happened.  But, at any rate, any time one of my dogs exhibits a new behavior that seems to indicate pain or fear, I make an appointment with the vet.  It's always a good idea to rule out any physical reason for the change before assuming that it's behavioral.