You're givin' Wolf a run for his money with this whole DIY thing aye...
I've found that digging wet clay is easier than when it is dry and feels like solid rock! Of course, it is heavier but easier to stick the shovel in.
And remember take it slow and easy, better to take a year digging up your pond than mucking up ur back!
Good luck and make sure you show us what the end result of the pond looks like.