rope attached to nabobs coffee can (or any coffee can) and beef heart placed in coffee can pointed towards shore in a foot of water or around that
I used to do that but its been awhile since ive trapped leeches for bait, we would always mark it with somthing to just so we would know where it was.
Theirs was always lots of leeches attached, And we would always check it the next morning. (This was in a lake)