Round jeweler's file and bore brush
The number one reason for ferrules pulling off a rod is glue failure. Regardless of the glue or epoxy you are using its a good idea to give the adhesive a bit of "bite" on the inside of the ferrule. The round file does a good job roughing up the inside surface of small ferrules and the bore brush works great on larger ferrules. You don't have to go too crazy with this process, just put some light scratches on the inside before mounting. Also, be sure and clean the inside of the ferrule with a Q-tip and alcohol after you are done.