Series 3 Under wing splash guards

I am looking for suggestions for improving splash protection under the wings.
I have the standard splash guards fitted, but they do not cover everything. See photo of driver's side splash guard.

I am looking as far as possible to keep water and muck out of the gap between the wing and the side of the footwell. I would also like to keep water or stone impacts off the bottom of the footwell.

I bought a sheet of black corrugated plastic from Wickes. This is intended as a building material, but I chose this as it can be easily cut and is flexible. My plan was to use this to cover the unprotected gaps.

Unfortunately, the problem if fixing it into place. I would sooner not drill holes into the wing panels.

Does anyone have any other suggestions?

Thanks for any replies.

There are plastic protectors! Mine originally had them attached to the splash guards! Although I'm not sure if they are still available?
Chris

When you fitted the splash guards did you put a spacer between them and footwell.
This seems to be the best option either a couple of nuts or some washers this allows the crap to fall through the gap so not build up and hold moisture