Try using your locator to see if the ferrets are working the tunnels underground. It will take time for a ferret to actually learn its job but the more you can work them the better workers they will make. I put one of my last years kits into a small warren last week and it ran through all the holes without finding a rabbit, i then put in my best worker and she bolted two. All ferrets will run through the holes but they wont search for the rabbits until they are actually looking for them