Elizabeth,
 
You can get Marshalls ferret bell collar at The Ferret Store
(theferretstore.com) for $5.87 each.  These are the best.  My eldest
ferret is now over seven years old, and has worn the same Marshalls
collar since she was a kit.
 
I wouldn't let my ferrets out without them.  The bell has saved one of my
ferrets from the dishwasher (thank God!), and more than one weasel that
managed to slip out the door over the years.  The bell also keeps a ferret
from getting stepped on when he walks up behind you.
 
I keep the collars loose enough (but not too loose) so that my ferrets
can slip out of them if they get hung up, which does happen occasionally.
These collars won't strangle a hung up ferret, because they're too stiff
to get twisted when the ferret instinctively twists its head trying to
free itself.  The collar just comes off.
 
I also put little ID tags on each collar - just in case.  I get the small
round stainless steel tags from Speedy Pet Tags.  I don't use the s-hooks
(the tags would hang too low).  Instead, I slip the d-ring in the collar
around to expose the flat part where the ends join, open it slightly with
a pliers, and put it through the hole in the tag, then slip the d-ring
back to where it belongs.
 
Hope this helps,
Nancy and critters
[Posted in FML issue 3691]