Since they're mammals, a hot pepper spray should discourage them. Otherwise, get dog, I guess.
I gave my sister one of these:
http://www.amazon.com/Contech-Electr.../dp/B000071NUS
for her birthday, and so far it's keeping the deer and rabbits out of her garden. I thought one of you Mcgyver-types should be able to figure out a way to hook a recording of a dog barking or a snake hissing or something scary to a motion detector.