Maybe a paddle fee stamp would be easier to monitor/administer than a kayak fee stamp?
If that brightly colored red-blue-green-orange annual $20 fee stamp were stuck to the blade of your paddle, it would make you feel like you is getting your moneys worth with every paddle stroke. The more you paddle, the lower the $20/stroke/annual fee cost per stroke which lowers the price/stroke!
Plus, when the MP putt-putts past you, coming or going, you get in the habit of waving your paddle, so the red-blue-green-orange paddle stamp can be seen by the friendly police ...... so many happy paddlers out there today!
Own two kayaks ........ well ....... the stamp is on the paddle ..... not the kayak ..... so that's a price saving ..... there ...... the stamp goes on the paddle!