Father-in-law's knife problem.

[Danny Linguini]

Is appearance important? If not, hockey tape.

Duct tape would make much more of a fashion statement.

 

[rhino]

We really need to see the knife to make a proper suggestion.

 

[eveled]

Just filing rings around it would help. Use a round file or even a triangle file. It would look like a m3 trench knife from WW2 Then if even more grip was needed, O-rings could be stretched into the grooves.