Yeah that's my next idea... I have a whole bunch of slate rocks I can built little areas that I might could insert the food under just for the corys. Yeah and my corys have just about dug a tunnel under my drift wood already, but the bettas often go there to see what the corys are up to. My bettas are smart and pay attention to what the corys do. When a cory is stopped and investigating or grouping up in an area, the bettas immediately head over to see what its about!
SO now my plan is to put a couple of aqua stones in a clearing. Put food down, then cover it with a slate rock. The corys will be able to get in there to the food, and the bettas may be less likley to venture in such a tight space.... can't be too tight or the corys get stuck.