I made a ghetto ass rail out of some old pipe, I screwed the rail onto a 4 by 4 and filed down the edges of the screw heads, then I screwed on two 2 by 4's on the bottom to prevent it from tipping side to side. PVC pipe also works, probably better, because it puts less strain on the screws holding it in place, is cheaper to replace, slides well, and doesn't rust.