Don't know if it works for deer, but I've read that red pepper sprinkled around plants is supposed to keep squirrels away.
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At one time I had a lovely, picture perfect Doberman Pinscher,
who, unfortunately, was mentally retarded, and always hated
any plant (or even bikes) that we put in the back yard or dog
yard. She would eat the plants down to the bare branches and
spit out the leaves. The only thing that stopped her was hosing
off the plants and sprinkling Cayenne Pepper on them. That
was the only thing that got the message to my poor Hilda.