Day one: foster dog (Isaac) and my dog (Charley) growl and bark and gnash teeth at one another. Foster dog sleeps in cozy stall in barn, Charley sleeps in her own bed.
Day two: Isaac quits growling and backs away when Charley growls. Charley goes into sulk mode and backs away when Isaac comes near me.
Day three: Charley and Isaac play musical spaces - each vying to be close to me, each stealing the best space in the house when the other gets up for whatever reason. Dogs rotate between Isaac's bed, Charley's bed, sheepskin on office floor, sheepskin on bedroom floor, and spot in front of fireplace in living toom. Neither will stay in a room where the other is.
Day four: I sit at my computer with both dogs asleep on the floor by my chair, just inches apart - but each stubbornly turned away from the other. Every few moments I hear a low grumble - first from Charley, then from Isaac, then from Charley, then from Isaac, just to make sure I know how much they resent sharing this space.
By day five they should be best buddies.