Duct tape is OK, but gaffer's tape is MUCH better. Anyone who has used duct tape knows that it tends to leave a sticky residue on anything it touches. Gaffer's tape sticks as well (or even better) than duct tape but it leaves behind NOTHING when it is removed.
'Course, gaffer's tape is around $10/roll, but you get what you pay for. Permacel is a top brand for a buck or two more than others, but worth it. You can find the stuff at photo stores that cater to pros, as well as movie supply houses and online sources.