Once they are paired up, nothing will stop them from breeding except putting them in different tanks. They will even breed through dividers.
Unfortunately, an egg-eating pleco or catfish won't be of much help. It will keep you from getting tons of fry but they will still be aggressive all the time, and will keep trying to breed over and over again. Also, they tend to take it on each other when their eggs/fry disappear overnight... when I moved my Salvini pair recently from the pond (they had fry that I couldn't move with em) the male got incredibly aggressive and beat up the female badly, I had to separate her for a week or so to keep him from killing her.