With a business of ferrets, I have now got 5 of the little fuzzie creatures, I love them dearly, they are all so tame.
They showed me in the beginning were they wanted to go to the 'toilet' so the litter box was put their, eventually my son made me a litter box, as its much bigger than a tray.
If they had a mistake, which they did, and use another place, usually a corner, after cleaning it, I placed a cuddly toy there, that kept them from using the same corner again, and it worked well.
I am having a problem at present with the two new guys, Bonzo and Bobi they will insist on going just outside the tray at present, I havent managed to 'fix' this problem just yet, but I do intend on trying the same idea, so I'll get back with the result, here's hoping it works again, watch this space!!!