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If you don't have one, swing by your local hardware store. In the electrical section they sell junction box covers (4 x 4 aluminum plate). Probably cost you around $0.50. They aren't as sexy as the Motorcycle Night ones but they do the trick.
No, I've never seen a parked bike fall over in the field but I've seen riders turn too sharp or get throttle happy on the dew covered grass and dump it leaving the grounds . They had to try something really silly to do it, but somehow they managed.