I use the plastic wing tips but I have also used the Nylon string from brush cutters and glued it along the wing tips. It comes in different sizes and colors, even clear so it doesn't show. When I build my planes I add wood at the wing tips so there is some extra thickness at the tips for the wing tip protectors shown. I have even seen control horns used. Clear plastic from a soda bottle siliconed to the tip was often used on fun fly planes. I have covered the tips with four layers of covering before the final main covering, it works but like tape, it can't take too many wing scrapes on a hard runway before it wears out. A lot of ways to do the same thing.