I have never taught an emergency down for any of my dogs. I have taught them an emergency word which is something other then come or front. It is taught using the highest value treats and should be practiced often so they don't forget the word. It is something that can be trained, all three of my dogs know the word, hopefully I'll never have to use it.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD