Ferrets are natural diggers, there's no stopping them except by
ferret-proofing the plant.  Even chopping off their paws probably wouldn't
help, they'd dig with their little stumps!  (just kidding, of course)
 
Here's what I did to each of my large pots on the floor: Get one of those
clear plastic trays that's intended to sit under the pot to protect the
floor from moisture.  With a storng scissors, cut a slit from the outer
edge to the center of the tray, then cut a hole in the center just large
enough for the stem of the plant.  Fit the tray over the pot, inverted (so
the edges hang over the rim of the pot).  Use clear packing tape and tape
the slit closed, then tape the tray to the pot all around the edges.
 
This worked great for me; my guys never got into the plants again.  It
makes watering the plants a little tricky, but with a watering can, I can
fit the narrow spout into the hole around the plant stems.
 
Good luck,
Nancy and critters
[Posted in FML issue 3678]