I added used chain link fence that projects 2 to 3 feet below water line along the bank. Very effective at stopping the rats. I put it in when the pond was new. Would be a greater chore now with the vegetation grown in. You could add it after the repairs to prevent a repeat.
I got it from a friend in the fence business. Now days the used fence has a high scrap value so you may not be able to get if for free.

2/3 acre pond 12 miles from that big pond we call Lake Erie.