Yes that is a fox - the tail and it's stance is that of a fox.I think it is plenty tall enough to be a coyote - here is a fox that just ran past the same camera. He is a bit closer in so is a bit more foreshortened but even allowing for that the other critter is way bigger.
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It could have been a coyote, it moved in a more dog like fashion. Have you had any issues with any unknown predators there?