I believe I can solve this case! *puts on Sherlock Holmes hat*
Do any of your neighbors have a dog that constantly escapes, a Houdini Hound you might say!
Maybe after one of your neighbors had a rather messy masturbatory experience it rendered the self sexing aid looking somewhat like a butchers bone... You neighbor possibly failed to place it back in it's appropriate place. The dog upon finding it was compelled by instinct to take this "bone" and as it was not hungry decided to bury it for safe keeping.
But this time the dog for some reason could not hide it's bulbous bounty and decided to hide it's prize outside his confines leading him to your front lawn!