Mommies, HELP!

So I am asking for help and hoping that someone has an answer to my problem! My child is fascinated with standing up in the bathtub and just won't sit down and take care of business. Once he attempts to stand up, I politely ask him to sit back down and if he doesn't listen then I try and sit him down myself and it is at this point that he locks his knees and just lays down in the water. Justin and I are big believers in letting Kaden fail at something to learn his lesson and that has worked on so many occasions. Like when it came to crawling up the stairs or going down the stairs, we were right there beside him but we let him make his mistakes and he has learned a lot quicker what he is to do and more importantly what he is not to do. But when it comes to bath time, we can't really take this approach since we are dealing with slippery surfaces and water. So what does one mom do? How can I entice my child to stay on his bottom while we are scrubbing the dirt off him! We will try anything!!