Answer: I have spoken with people who say this worked for them. The point is not that the deer can't learn to not lick the peanut butter, but that the experience of the shock gives them a general fear of the area. Perhaps they don't associate the problem with the peanut buttered foil as much as with the general area.
I have found that things that worked when deer were only curious or marginally hungry fail when they get hungry enough. In other words, hunger expands their palate and increases their bravery. Therefore I wouldn't be suprised if the peanut butter and foil system worked primarily when deer "pressure" was low to medium.
Thanks for the question!
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