Bummer on losing some fish! Hopefully you re-stocked them as fast as you could grab them.

Lesson #1. Did your normal pond outlet get plugged? If the answer is yes, then you need to determine the cause, and fix it before the next frog strangler rain.

If the answer is no, then your outlet is undersized. That is difficult to fix in a filled, stocked pond. I would recommend reading some old threads on installing a siphon outlet system. That can be added to an existing pond and can be sized to handle the flow into your pond.

If your pond is connected to a stream or waterway such that any big rain will cause the water level in your pond to go over the emergency spillway, then you probably need to build a diversion works for the stream to bypass your pond. You can size a pipe through the diversion to only admit a fixed rate of water to enter your pond.