Here is one of Dad's old time free trapping tips;

OTTER “ALL CALL’ SET
A big problem in otter trapping is to make one’s sets so that they overcome the otter’s swimming with its front feet folded and rear feet extended back and out.
Here is a set that overcomes this. After locating where otter frequent an area, locate a place where the water is 10” deep and the bank is at least 2’ high. Dig a hole 6” in diameter, 15” deep into the bank and 18” above the water line. Set a very well covered trap directly below the hole and one foot out from the bank. Use a quantity of Lenon’s Otter Super All Call lure the size of a large bean on a twig or chip and place it a foot back into the hole. Place the same quantity on another twig or chip and pin it to the bank six inches above the hole. If bait is desired, fresh fish or a fresh shrimp is the best bait. Place bait in the very back of the hole.
When otter investigate the hole and lure, the water is deep enough so that the trap is not sprung by the otter’s body. As the otter places its front feet on the bank to peek into the hole, it will drop its rear feet to the bottom and into the trap.
Herb Lenon - 1950

I always thought they were on the small side also till I caught one in a set I had made for mink, it was stone dead and the area was not all tore up. This set was a hole in the bank, there were two of them, I set a trap in each one. Came back three days later and had an otter in one and a red fox in the other. I use this spot every year and have caught several otters in these same holes. Since doing that I have now used 160's on purpose for otters in other situations such as dam cross overs, trials coming or going from water and found they work well. I only have Belisle 160's, I have never tried any other brand. Now that being said, if a 220 or 330 will work at a set that is what I use. But in certain spots to small for a 220 or 330 don't be a fraid to use a 160 it should do the job, Belisle's do. 220's work very well for otters, I don't feel they are to small for otter at all. Crutch

Thanks for everyones help! now mabey ill be putting an otter on the board next season