You are right..temperature is the key. Goldfish must have a chilled period. Do your goldfish stay outside through the winter in your pond ? Ours do, and they are very prolific !!!
May I ask why you drain your pond ? Our ponds are inground and at least 20 in deep...I have seen several inches of ice on them some winters...doesn't hurt a thing. We never drain ours...it takes too long to get the balance back.
If you want more fish babies, you will need to leave them in the pond through the winter, or go buy you some new goldfish in the spring !
Goldfish will eat their eggs, and frogs love the caviar,too! Some extra greenery for the eggs/fry to hide in will solve that problem.
Hope this helps...I don't want you fretting over fatherhood !