Probably the only way to stop it is to separate them, and I know that cages are NOT inexpensive at all! But separation has worked for us, even if it is stressful at first for the birds (and noisy for us). Since Bennie is using one cage, and Roger and Milly, the other, their mating habits have started back. I may have to take Popcornbird's suggestion and put Milly with Bennie and keep Roger by himself. Milly laid a third egg during the night last night. I'm going to start pulling them, one by one, later today. Makes me sad, but I would be sadder to have more babies.