The more you handle him the faster he will grow out of it.
I had my ferret trained to guard my office..If you went in without me or my wife you the **** bitten out of you until you left the room.
This used to hang on my office door.
Unfortunately Mr Spot passed away 3 years ago. I still have the warning on my office door. Mr Spot was a Silver fancy ferret. He was the coolest.
I'll post a few pics as soon as I find the disk with them on it.