All the above ideas work well. One of the neatest working devices I have seen were soda pop bottle cases. Years ago I came to a pond with several wooden pop cases floating upside down. I picked up two, looked inside, and each hole had a fathead nest. Visual barriers made a difference. Nowadays, many plastic pop bottle cases aren't solid, but if I can find one which is, it will have a new, wet home.

Teach a man to grow fish...
He can teach to catch fish...