If I were doing it, I'd lay that stencil on top of green fabric and trace all of the snakes with fine chalk, press that fabric onto a Steam-A-Seam interfacing backing, cut them all out, press (with an iron) them on to the shield cover, then go around them all with a medium-sized satin stitch. Permanently sexy shield cover = awesome. Perfect edges also = awesome.
Similarly with white fabric for the skull.
See:
![Image](https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-ash2/33446_667121356338_4704239_37557276_4770794_n.jpg)
This shield cover I did for a guy with Helm's symbol from the Forgotten Realms on it.