So here is the low-down:
We've got a 9 year old Blue Heeler mix, neutered female named Millie. We've also got an 8 year old full blood Heeler, neutered male named Ryley. The two of them have always gotten along - she is the dominant, but mostly just ignores Ryley until he really gets on her nerves. Then there is a brief "smackdown" wherein she reminds him who the real boss around the house is (dog-wise that is).
A couple years ago we tried adopting a 2 year old lab mix - had him neutered and all. Despite trying everything we could think of or read about, we could never keep all 3 dogs in the same room together. They got along in all combinations of 2 dogs, but when all 3 were together, Ryley would attack Nox (the rescue) until one or both of the two were bloodied (Nox wouldn't attack first, but he wouldn't back down from a fight). We ended up finding Nox a new home
Last year we decided that we would probably be safer in adding a puppy, so we got an Australian Shepherd, Tucker (just now a year old neutered male). All three dogs have been together from the day we brought Tucker home, and 90% of the time everything is great. We've had the occasional spat over food and water, but adapted by everyone eating/drinking in separate locations.
And finally the problem - lately Ryley has been going after Tucker more often (basically given any reasonable-to-dogs excuse - he licked my water drop, he looked at my bone too long, etc). Tucker doesn't start the fights, but he will start the defensive growling, and he will pursue Ryley once I've pulled them apart.
My questions: Am I better off letting the two of them work out their own position in the hierarchy? I will be working with both of them individually on basic training (new stuff for Tucker and reinforcement for Ryley), anything I ought to try specifically? Tips from anyone in a similar situation? Stuff that has worked for you?
We live in the middle of nowhere Texas, so odds of finding a qualified trainer or behaviorist in our area are pretty steep.
Thanks in advance!