I saw chet go to mark a post in a rental unit told him no, and outside gruffly and shut the door. He has never tried to mark in our house.

Even when I finally left the door open for him he wouldn't come back inside. 

I gave him a release command and he came in. Since he was acting confused, and to test a suspected possible trigger, I called him close to the post and let him smell the rag I had cleaned it up with. 

His hair immediately started raising up, speaking very softly I told him no, and he started growling. I usually don't use hands much to gesticulate when talking, but I intentionally did with him today and everytime I moved my hands when I said no he would growl a little more intensely.

I gave him a sit, which he obeyed, showed it with him still growling and continued to talk softly, pointed to the post said "no, outside" and wallked him out. He is an exceptionally smart dog so thought maybe could convey a meaning. Lots of what I was saying was gibberish just to work past the trigger and increase trust so he will know I have no intention of "man handling" him.  I continued to use my hands while talking just far enough away from him he didn't feel a need to defend himself gradually working closer.

My not being the least bit angry or aggressive towards him seemed to keep him confused and interested at the same time.

Brought him back in and repeated, even though he was still growling, his hair wasn't raised near as much and since some of his breed will "talk back" moved quickly with my hand toward him. By then I was close enough while talking I was almost touching him. Actually had a little play session. 

Currently I have no fear he will attack unless I actually make a fast move for him. His behavior so far has been defensive in nature, with the definite impression as he doesn't expect to be able to escape it so stop the attack if it comes.

Repeated again. No growling this time. 

Not sure what took place in his mind, but his look was completely different, and the way he was the rest of the day was much more relaxed and his interest in watching what I was doing more prononced, and wouldn't get more than 10 feet from me the rest of the day.