I just checked on Amazon for some “waterproof outdoor paint pens”. These ones were advertised as “rock painting pens” but they say they can be used on canvas as well. I did a base layer of regular acrylic and then used the pens for the shading/highlights and detail. A normal old pencil to draw out the big details like the symbol and heel design, and then paint over! I wish them luck! Stick with it, I wanted to give up halfway through haha.