Corner deterent- The pepper might work.  I have tried a variation of your
pepper method and it seemed to keep the ferret away for the most part.  Now
I place a bundled towel or blanket in the corners I do not want them to use.
They think the corner is a bedding area, so they use another place.  So far
it has worked more than anything else.  I just have to watch out for when
they drag a small towel away from the corner to play with it.  But your
pepper idea seems great!
 
Carpet scratching-  I have a squirt bottle filled with water.  When they
scratch or try to enter the fireplace, I squirt them on their torso.  If I
squirt their face they think it's a game and jump at the water or the bottle.
 Now the only thing they scratch is the front door mat, which can easily be
replaced, but has yet to show any signs of wear or tear by the ferret's
scratching.
AntsLove
[Posted in FML issue 1340]