Tienes una memoria de elefante.

English Translation

You’ve got a pretty good memory.

Why not make this an exact translation?
So the English could be “You have the memory of an elephant.” instead.

It’s better that idioms/expressions be translated in a more universal way, otherwise the meaning is lost to those that don’t already know the phrase.

For example, I’m learning Spanish from English, and one of the sentences is estoy en el quinto pino. If the cloze was: estoy en el quinto ____ :: “I’m at the fifth pine tree” Then I would answer correctly, but I would have no idea that this is an expression like “I’m in the middle of nowhere” (locally, in Spain)

Good luck with your studies!