A little more information might be required such as size of tank and if there are any other occupants. Is this a FO
or reef tank? If you had the clown for 4 yrs I will assume it is fairly large(5-6"?). If the tank is large enough I would suggest re-arranging the rock work or adding additional racks if that is an option. Then reintroduce the clown. Maroon clowns are known to be very territorial and should be one of the last fish added even when a juvenal.
This is just my thoughts, others might have some other ideas. I am currently keeping a pair of Maroons in a 75gal with other fish successfully, but the other fish were added first.