A buddy told me this and I tried it on every dog I've had since.
Take a biscuit, show it to the dog, put it on the floor and then
put a light weight plastic bowl over it. Not a transparent one.
My smart dog wasn't fooled, and knocked the bowl off every time.
My 2 dumb dogs - hard as hell to train them anything - never had a
clue. The biscuit never existed once the bowl went over it.
Anybody care to give it a try?

--Vic