Carpet caster cups

Not only are carpet caster cups good for keeping wheel based furniture like a bed from rolling around, they also help to protect your carpet from being damaged by heavy furniture. A quality carpet caster works to distribute the weight of the furniture evenly so no one particular carpet area is left with a permanent dent. This works great for both thick and thin carpets regardless if the furniture has wheels or not.
Carpet caster cups:

Carpet caster cups pictured:
Left: Slipstick CB420 Carpet Caster Cup, Clear, Large
Right: Slipstick CB410 Carpet Caster Cup, Clear, Small