I was having trouble keeping the Dunks where I wanted them.
They would wash out of the containers, as I have 'crock pots' to catch the rain water from the gutter down spouts.
First try was to place the Dunk in a plastic container with holes punched it but it still floated and the young pup would 'bob apples' for it.
Second and current attempt is to put pieces of the Dunk into glass salt shakers. When filled with water, they stay put in the bottom.
To minimize the corrosion to the metal cap, apply some WD-40 or Vasiline each time the shaker is re-filled.