I made this cat toy for my cat a couple years ago. She was playful today, so I took the toy out to see if she still likes it. It turns out she still loves it! From her immediate reaction, I would guess that the catnip inside still smells fresh and yummy :)
The toy is knit in wool and then felted. The felted wool makes it very durable, although my cat does tend to be gentle on her toys anyway.