Last night, after moving my tank(s) 200 miles, I set them up and went to bed. When I got up in the morning, Kamehameha was on Smaug's side, and Smaug was hiding near the bottom. Smaug is fairly shredded, but it is all fin damage, not bodily damage. He was really upset, just staying at the bottom, but I figured it was his ego, not anything else. So I shooed him out of his hiding spot with my hand and fed him. Truly, the way to any man's heart is through his stomach! He is back to patrolling his territory, even flaring at Kamehameha. Phew. I am glad that my two are fairly mild mannered fish.
As for how the divider failed:
Well, there is a giant hole in it for the giant rock. The rock must have shifted about a cm over and that left a gap just big enough for Kamehameha to squeeze through. It was easy to move back, but it doesn't look the same any more. The divider now is visible when looking at the tank straight on. I will be growing the Christmas moss over it, so it should not only look better (even better than before!), but also create a buffer in case this ever happens again. The moss will be able to at least hide any holes, if not fill them in completely. They also won't be able to see each other any more, once it has filled in.
I am actually happy that it failed where it did, not at the sides. I knew I was taking a risk when I had the rock in there, it failed because I did too much in one day and didn't check everything close enough. It was late at night when I got home, and I just wasn't thinking.