Shovel. Barbeque prongs tied to a stick. Pin head down into grass, cut off head with shovel, knife, machete, etc.

I had a friend that made a snake killer while he was working oil fields in Wyoming. 3-4 ft length of pvc pipe, long piece of wire doubled up and pushed through the pvc pipe. Make a loop with the wire, get snake head in loop, yank the wire out of the pipe with force and cut off snake's head. Should be relatively easy to kill them.