Shielding for Aquaboy Modulation

[Bio77]

I'm planning on building the Aquaboy with the added modulation board.  Since the boards are stacked on each other, I'm wondering if shielding between them would be a good idea?  Haven't built it yet, so, don't know if this is a problem. 

I have built other stacked pcb designs (e.g., Dead End FX FL99) and LFO noise is definitely present.  I've been thinking some shielding might improve these too.

I'm wondering how to implement this, any advice appreciated.