Take a small clear crystal, an acorn, some rosemary and mandrake and a bit of green silk or cotton. It doesn't need to be a big piece. Cast your circle and creating a pouch from the herbs, bless them with each element saying:

"While this dwells within,

"There will be protection without.

"Cleanse and charge this charm,

"Element of against all who wish me ill!"

Now hang this somewhere not too obviously, like hiding it in a corner or over a window. This will protect you 'til next Samhain when you should burn it in the sacred fire, crystal and all. If it is not too tainted, the fire will just cleanse the crystal and you'll be able to retrieve it from the ashes but I always recommend just getting a new one.