How To Separate Gravel From Sand

[SensesFail]

I'm wanting to create a milawi tank I currently have gravel in the tank and ocean rock on the way. I was considering doing half and half with gravel and sand to get sort of half marine like and half river like with a plastic plant or 2. Not sure how this will look so any suggestions will be greatly received!

Onto the all important question. What's the best thing to use to separate the gravel from the sand? Otherwise won't the sand go everywhere!?

Cheers guys

 

[doresy]

Sand and gravel will always mix up in the end.

Coral gravel produces sand in time in a natural way.

 

[Squidward]

Malawis like to dig and excavate. Won't be long before the 2 types of substrate get mixed.