Dawn,
 
I can only tell you what I know based on experience with my own ferrets.
Others may have different experiences or better-balanced, less curious
ferrets.  I have two leapers in my bunch.  They will leap over great
heights (okay...not that great -- from the futon to the table tray)
without regard to their health and longevity.  If I'm not wary of where
I put the table tray, sometimes I'll hear a hard phumfpt, and see a
confused ferret.  We have hard wood floors, so even with little things
like that, I must be careful.  I had tried to train my fuzzies to sit on
my shoulder to walk around with me.  One does really well all the time.
Another does well until she sees something interesting and she'll start
walking right off me.  The other just walks right off of me and would
fall to the floor if I weren't careful.  She hates being held at all and
will try to break free no matter how high.  (I don't even bother trying
to carry her on my shoulder anymore!) It's either no natural fear, or
(more likely) she just can't see that far.  From what I've heard, ferrets
are very near-sighted, so they may not even be able to see that far down.
 
So, personally, I think you'll have to find a way to block that area.
Ferrets aren't as well balanced as cats -- well, mine aren't.  And I
could see one of mine finding something interesting to jump to from the
cat walk.  As for the stairs themselves...we have stairs and railings.
The only spots we've had to cover are those that gave enough access to
something interesting below (our turtle tank).  Otherwise, our ferrets
have shown no interest in jumping through the railings.  Although, we
do have one that always likes to take a peek through them.
 
Best of luck,
Suzanna Donahue
[Posted in FML issue 3975]