Nyles is right. Try this. Take a sturdy rod and reel, set the drag to where the line just can be stripped off without breaking the line. Use a heavy swivel, [not a snap swivel] tied on the end of your line, attach about a two foot steel leader directly to the swivel, hook and bait the other end. Tie a clothes pin onto the jug with a short line. Clip your fishing line with the clothes pin so that your bait hangs the same depth as it has on your last two sets. This will allow whatever that has been taking the bait to do so again, only thing, when it does, you will have him on a rig that will hold him and one that will allow you to reel it in the next morning when you check it. Also, may I suggest that you try getting up and checking it around daybreak. Be sure to use tackle, line, rod and reel of sufficent size to hold whatever you feel has been taking the bait. From the size of the pond, it could be a big cat, but, my guess is, it is a big turtle or a gator.