If you put large slate around the perimeter of the pond, let them overhang the edge a few inches toward the center and 5 inches or more above the surface. The raccoon will climb on, but since there is no "shoreline" on the edge, to reach safely in for a meal, they run the risk just plain old falling in.

This method looks good, doesn't cost much, and it has worked for a couple ponds I have done - one in Calgary back in the day, and one in Brookswood in Langley.

Just make sure the rocks, or whatever you are using, are sturdy.

Good luck, and keep us all updated