It's happened to me a few (but not many) times - always a complete surprise and not noticed until I get home and usually happens on group rides where we've left the road for a bit (like going through a park or taking a walk through some woods). I use the hose on it combined with a scrubbing brush. Once I had to remove the cleat because the s***t was too stubborn and too worked in. Then the disposable gloves and disinfectant came out. I put a piece of duct tape in my shoes over the slots but under the insole to stop water ingress from the sole - this makes me feel a little bit better.