Recommendations for Riding Kit in the Rain?

I haven't ridden in decades and to be fair was just a kid when I stopped. We picked it up again and went horse riding this weekend in the heavy rain. Really, I don't mind the rain, but I was wondering if anyone here might have advice for what to wear when it's going to rain other than normal rainwear? Even wearing a rain shell and decent boots, I got absolutely soaked from head (well, not under my hat) to toe. Thank goodness it's summer! :-P