I did kind of an 'alone training' when Triss was a pup. (This was advice from other YTer's at the time.
) I would at first leave her alone for 15-20 minutes. When I came back, I wouldn't make it a big deal and she wouldn't get any attention right away. I would increase the time alone slowly over time. Now, she is a year old and she is fine when I leave for a few hours and come back. She does get excited but has learned to 'contain herself' until I come to say hi to her. She also sleeps in a separate room at night in her xpen with Spike. I think that has helped a lot too.