Alternative 1 to conventional guardrail
First I have bought a 3 - wire ribbon cable and a round aluminum tube at the hardware store. The aluminum tube I cutted into 3.5 cm long items and then I painted the items and the ribbon cable gray. Now I screwed the 6 cm long screws through the plywood- and chipboard. About these, I placed the alu items and glued them with superglue. Finally I glued the ribbon cable to the alu items and fixed the cable with clothespins. You also can fix the cable with small screws.