There is a wide variety of harnesses, for example the Vac-U-Lock
Harness system with the Ultra Harness for men and women. These
harnesses can help hold the following extensions in place. For
men there are rubber and jelly prosthetic strap-on penis
attachments for an erect or non-erect penis to insert. There is
also a soft latex vibrating prosthetic penis attachment
extension to lengthen the short penis. For women some of the
cyberskin realistic cocks and most of the jelly realistic cocks
are harness compatible. Harnesses come in leather (most
expensive, last longest), rubber and nylon (least expensive)
versions. Attachments can be regular or vibrating. Prosthetic
penis extensions are quite inexpensive (under $20), as are the
simple harnesses for them (from under $30 up to $100 for
leather). An interesting variation is the strap-on dildo that
goes on your chin!
Instructions for the Ultra Harness: "Securely strap on your
secure leather harness then attach any of a selection of dildoes.
This harness has an adjustable waist up to 44 inches, an open
crotch for maximum comfort, easy access, and non-slip action;
all designed to give you command and control for your erotic
pleasures. The Vac-u-Lock plugs attach with velcro or snaps.
This Harness can be used by women or men. The opening under the
plug is high enough to allow the man's penis to hang below."