fishing rod is a reasonable idea but the issues with that are the line will require some weight to cast out so your risking damage to the boat should you accidently hit it where as a tennis ball will bounce off, the other issue is if you cast over the boat and the weight sinks as it will, should the weight snag on the bed you not only have a stuck boat but a stuck line to pull in, and worst case if it dose catch the boat and then snags up you have to pull the line risking serious damage to the boat should the line ping back or worse sink the boat if its not quite sealed for a capsize, where as the tennis ball floats and it soft.
the advantage over the ball method to a rod is that you have to carry extra in the car such as the rod, and a reel set it all up and it all takes up room and is not a quick retrieval, where as the tennis ball and rope method is a small box bundled in the boot for quick retrieval (just make sure you don't bird nest the line!) , remember next time it may not be a cut out it could be a fire of sinking! 10 mins messing about with a rod and your boats sunk and lost, at least with the ball you have a few mins to attempt to get it quick.