Folding covers are available with hard plastic or aluminum panels, or soft, vinyl covered sections that fold up toward the cab. A hard folding cover that can be locked is a good choice if you want optimal bed security. One of the most innovative soft tonneaus available is a combination roll up/folding cover that can be rolled open from the rear but also has a hinged front section that folds back for quick front of bed access.
Another type of hard cover that offers security is the retractable tonneau cover. These tough covers feature rugged aluminum slats that work like window shades, sliding on rails and rolling up into a canister. Retractable covers can be locked in incremental positions, exposing only as much bed as you want, and some are available power operated by remote control.
