If your target pest recognizes foxes as predators this product may be effective in keeping those pests away, but if you have not had any foxes around long enough so the target pests do not recognize them as predators they will have nothing to fear and the stuff won't work, no matter what the hype says.
Last summer we had both foxes and coyotes around, for a while, but evidently not long enough to reduce the population of rabbits, squirrels, chipmonks so none of them developed enough fear to change habits in any way, other than to be a little more alert when the fox or coyote was nearby.