Kelly,I have seen clear vinyl walk way (runner) mats used in koi ponds.The traffic side was installed face down and the small cleats faced up to help hold rocks in place.Carpet will not last among other potential problems and may become a problem in short order I would think.Lowes or Home Depot or any flooring place will have rolls of this to custom cut whatever length you need.Rubber mats as Tentmaker suggests should work great also.Good Luck