I too have Otter problems in Northern MN. I have a 7 acre pond, they have been coming and going for the last three years or maybe longer. I am never there to try and shoot them but I have done a lot of research and I am going to fence it of with 3x2 inch Galvanized mesh fence, plus I will put a live wire around the top of the pond, at this stage I think it will cost around $3500.00 but in the long run will be well worth it. I will put the link on here so you can see what I will be [url=doinghttp://www.electricfence-online.co.uk/shop/electric-fencing/][url=doinghttp://www.electricfence-online.co.uk/shop/electric-fencing/][url=doinghttp://www.electricfence-online.co.uk/shop/electric-fencing/]doinghttp://www.electricfence-online.co.uk/shop/electric-fencing/[/url][/url][/url]

I hope this helps, they say an adult Otter can eat 10 Lbs of fish a day, they hunt in pairs and when they are full will kill fish just for the fun of it. Let me know if this helps, I will post some pictures of my project once it is completed.
Thanks