Irena,
I feel that a collar of some sort is a necessity with ferrets.  It is both a
way to identify them as pets and something to attach the ever helpful bell
to.  This way you usually have a clue that they are around.  That is unless
yours is like mine and eventually learned how to both walk and run without
letting it jingle (stelth mode).  With one of mine it took a couple of weeks
before he was finally certain that I would keep putting it back on (I had
two so that Taz had one on while I searched for the other one that was
hidden).  After that he doesn't take it off much.  TJ never really tried to
take it off once I got it sized right.  You need to be very careful that you
don't get them too tight.  Fitting them is a tricky game.  You want them
tight enough that they don't just slip out of them, but loose enough that if
they get caught somewhere, they can pull their heads out.  I found that at
the right fiting, I could put one finger between them and their collar.  I
also found that I had to sew (about two stiches) the collar to the right
size, because they could make it bigger by scratching at it.  Just give them
some time to get used to it.  I Hope this helps.
 
Ellen, Taz and TJ
[Posted in FML issue 1484]