An inexpensive marker buoy can be made with a 2- to 3-foot section of 4-inch-diameter bright-yellow foam pool noodle.
Poke a hole a couple of inches from one end, and tie a loop of 1∕8 -inch nylon rope through the hole.
Attach a large snap swivel to the loop, then a measured length of nylon line, and end with a sash weight or multiple sinkers wrapped with duct tape.
Mark the line length on the side of the noodle with a felt-tip marker.
The line wraps around the noodle and unwinds when the noodle is tossed from the boat.