Of course ya'll are talking about the 5 year old neutered male, right?

I was hoping so. I still really don't think the 4 yr old is the instigator, I just thought he was giving off something to set the other one off.

I do have the pack structure dvd, (which I should probably watch again, its been quite a while) building drive and focus, marker training, obedience, raising a working puppy, e-collar, crate training, and more, watched them all (except the dog aggression one) plus many books.
I don't run a super tight ship, but it isn't terrible either, but I thought I was doing fairly well. This issue isn't great. They aren't constantly trying to kill each other on sight, thankfully, at least not yet.
I know there is a problem, but, I don't think toys are it as far as a resource guarding problem. Toys aren't laying out. We take the chuck it, or frisbees into the fairgrounds for fetch. Then toys go back in the box. And usually they are taken out individually, I like individual playtime with each dog. Every once in a while it is fun to take 2 out. One ball goes one way, throw the other ball the other way, it's nice, it's fun, they have fun. That is our toy time.
Two dogs are normally crated at a time, one dog with me in the office/store and one is outside kenneled/or loose in the house. Then they get rotated during the day. Sometimes 2 are out together. The girl can be out with anyone, she is a sweetie.