My Jag has gotten real agressive since i got rid of the Giant Pacu that was in the tank.
He and the Jack Dempsey have been battling pretty harshly. The JD is smaller, especially when it comes to mouth size, but man, that JD is one FIERCE mother f-er.
My solution was this: Caves. I got 4" PVC pipe fittings and stacked rocks to hide them. I don't know if Dovii are territorial or cave dwellers like the JD, but when he is in the cave he is safe. All he has to do is guard it. He chases the Jag out without much of a problem.
Over the course of about 30 hours before the tank was rearanged, the JD has a few small fin tears, and the Jag's lower lip is pretty chewed up.