When we gig bull frogs we always check the stomach contents when cleaning them. It's amazing what they will eat. We've found that there favorite meal is small bullfrogs. We have also found water snakes, baby painted turtles, rats, fish including a 9" Redfin pike, bugs and birds. If it fits it's gone. But the fact that they eat there young may explain the lack of young frogs.
I've found many of the same things you mention. They are voracious and highly predatory. Back when I was bass fishing a lot, I would catch them fairly regularly on topwater jerkbaits.
If they could achieve a bigger top-end size, it might not be safe for your terrier to visit the pond alone.
