I was at a wedding this last weekend (a lovely do - congratulations Mr and Mrs Ross!) and there was one girl who was wearing one of the best inventions I have ever seen. 

They are called heel stoppers and they basically stop your heels from sinking into the grass!!! How clever is that!

You slot what looks like a mini clear funnel over your heels and there is a little plastic disc (again clear) at the end which stops your heels from sinking into the ground. 

A quick Google shows that they are quite reasonable in price too!!