I have a shallow 8acre pond that is being over-run by muskrats. They chew holes in the levy and damage the outflo, as well as chewing a hole in a zodiac boat ($$$$$).

The previous owner put out traps and said he removes 50 musk rats each year, but they are back again next year.

What can I do to safely get rid of them? I hate to resort to the leg traps the previous owner used. Is there some chemical that is safe to use?