This is a bait bucket rod holder. It combines the convenience of a rod holder with the functionality of a bait bucket. The water and bait in the bucket functions as a weight to hold down the rod when a large fish hooks on , ensuring you don't lose your catch. This is a picture of the final product.
Here is a link to another design:https://www.instructables.com/id/How-to-make-a-rod-holder-bucket/