When my friend Eric got married it was a beautiful outdoor ceremony on a mansion property with beautiful green grass everywhere. Because I had a small part in the ceremony I wore my heels to look nice for potential pictures. Unfortunately the entire night my heels were sinking into the damp grass and the way it made me walk I probably looked pretty dumb. Luckily my shoes were black otherwise my heels would've been stained a muddy brown. What do you do about something like this? Especially if you have to wear heels during the wedding?
Have you heard of SoleMates? SoleMates cover the base of the heel to increase the surface area of the heel to prevent sinking yet it remains flexible for walking. My first impression was that it's really ugly. Haha but you've got to wonder, "How often do people look down at the back of your heels?" SoleMates would be great for brides and bridesmaids in heels with outdoor ceremonies. The length of a long dress or blades of grass would easily camouflage the heel of the shoe. If it's within your budget consider having SoleMates for your guests to protect their shoes and their balance.
Update: After reading Kristin's (hihi!) comment I was reminded of this chart. Apparently SoleMates offers different sizes. I don't know why but this info wasn't on their "Products" page but on bottom of their "How it Works" page, here. Weird.