Fraser: maroon clowns are more aggressive to begin with, but are they "fighting" in or around an anemonie or out in open water? If they are fighting in the anem...it is usually just the dominance dance and not much to worry about--except for the anem. From time-to-time the clowns can become a bit aggressive and end up killing the anem. I have a pair that fought for days in the anem and ended up kiling the sebae. I have another anem that was in the tank that they have left alone. They fought for a week and I thought for sure they were going to kill each other, and they had been together for some time and the anem brought out the worst in them. They are back to best buds...but one has obviously taken on being the female and is larger.
It is a bit un-nerving, but hand in there and they will get through it. If they fight in open water I would be concerned....IMO. And by fighting in open water I mean not leaving eachother alone at all....just constant badgering. If it is limited contact, not to worry.
Let us know how they are getting along.