Agree with the above comments get covers but in your case don't stop in mud, you know its an issue so avoid it.
I have never had a problem in many years using SpeedPlay pedals but I also make sure I don't step in mud and use covers when I need to walk in them.
If you do take your water bottle and spray it out before you get back on.
This is a user issue not a pedal issue, if you always are getting into mud get the SpeedPlay frog series pedals.