These fish are the meanest geophagus I have ever dealt with. Are you sure you have a M/F pair. I got a pair a while back that turned out to be a pair of males. Needless to say, only one of those fish made it. You could try and build a breeding barrier with a smooth surface for spawning in between. I'm not sure if they will spawn from opposite sides of the barrier, but they are substrate spawners. Or, if your male is much bigger than the female you could put a hole in the barrier that only the female can go through. This way she can escape if she is being chased.