I'd correct Mason each time he tried to hump the Cairn. Doesn't matter the reason he's doing it, he shouldn't be allowed to do it. And it most likely won't subside on it's own and even if it did, for the Cairn's sake, I'd make Mason stop.
What's his name by the way?
And I'm sure the bite is probably in fact why the first person got rid of him. Sounds like he originated from a mill, then went to another and now he's w/ a wonderful family that he desperately needs and deserves!
Congratulations on the new puppers!
