Can Sharpie markings or decals be applied to the surface permanently? If so, what type of coating could be applied to enhance durability of said markings?

Unfortunately, there isn't any type of coating you can apply to this magnetic strip that will allow a decal to stick to it permanently. Decals may peel off over time. We cannot guarantee that they will stay applied to this product. However, Sharpie markings will not come off of this product.