Ha! I just came across 'Stray Dog'!
There he was just laying down in the middle of the stone bridge over the river just west of the Sarethi Farm.
There were no wolves attacking him or anything like that. I had heard that you saved him from attacking wolves in a random world encounter. When I pressed 'E' the choices were 'Wait here' and 'Go Home'. Apparantly he automatically instantly became my companion because moments later a bear attacked and Lydia and Stray Dog fought the bear. After the fight, Stray Dog came back and layed down in front of me at my feet. I don't know what the 'Go Home' command will do. I'll try it later.
When I eventually give him the 'Go Home' command, where will he go? The bridge I found him? One of the houses I own?
