I've gone ahead and updated scribble to allow scratching into certain areas with an appropriate weapon and tool. This will last longer than just the standard scribble in the sand and chalk drawings. The hardness of the weapon or tool will also affect the duration.
I've also increased the duration of chalk drawings compared to drawing in the sand with your finger.
Yes, I've heard the call for drawing with blood, but due to a lack of ways to obtain blood, I'm holding off on this for now.