www.mypleasure.com/education/sex-toy-guide/dildo_anal.asp

Whether you enjoy light or deep penetration, slim or thick girth, smooth entry or lots of friction, remember to select a smooth, seamless toy for anal play, one with a flared or larger base. Anal Dildo You don't want your toy to get lost in your rectum. Unlike a woman's vagina, the anal canal doesn't produce any sort of lubrication. The last thing you want to experience during anal play is the sharp, shooting pains that can accompany the insertion of a dry dildo. Take it slow, be gentle, and respect your partner's boundaries. While many kinds of Dildos can be used for anal play, you should always select one with a flared base so it doesn't slip in farther than you intend. The last thing you want to become is an emergency-room anecdote. For safest play, select a Dildo that has been specifically designed for anal play. Available in all sizes and shapes, Anal Dildos have a wide, flared base attached to a tapering shaft, which can vary in size and shape from a long, twisted phallus-shaped rod, to a short, stocky model that can be worn without restraint. Many people enjoy the sensation of fullness, similar to the sensation women experience during vaginal penetration. Other people employ a thrusting motion with their anal dildos. Just be gentle -- otherwise you risk anal fissures and a host of other complications.