Here is an otter set as described in one of my Dad's 1950's trapping tips literature:
OTTER ALL CALL" SET
A big problem in otter trapping is to make ones sets so that they overcome the otters 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 one foot out from the bank, directly below the hole, and one foot out from the bank. Use a quantity of Lenons 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 otters 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.
--Compliments of Lenons Animal Lures --