It seems you've solved your problem, but it's just worth noting that unless the day-care man states that "the two prefer to play with other Pokemon", they eventually will breed. And if you continue breeding with Ditto, you should never get this message unless you're attempting to breed with Pokemon in the Undiscovered Egg Group.
To make them stop producing eggs, just deny the Daycare Man as to if you want his egg, and take your Zoroark out of the daycare.
Hope I helped. :)