Just put them on tightly, it really is as simple as that. I dont know how so many people have problems with the old mk3 collars, they are wide so that they can go on tight without any problems. You will need to burn new holes in the collars though, put a new hole inbetween all the standard ones. Then just do the collars up as tight as they will go, within reason. They can be alot tighter than you think, you shouldnt be able to get a finger underneath, thats wayyy to lose. When the collars are on, pick the ferret up by the scruff above the collars and slide the collars down as far as they