To be able to trap otters, you must know EXACTLY where they will travel. I would invest in electric fence stakes and put a couple of strands of wire around the pond close to the ground, not more than 3" apart and go up at least a foot. If it was my pond AND I had power back there I would go with this one.
https://www.tractorsupply.com/tsc/product/power-wizard-pw9000-electric-fence-controller It's for moderate to heavy vegetation too, so you probably won't have to trim much around it.
I know you don't have power there (yet) but if there are Otters coming and hitting the pond; you don't know exactly where they are traveling AND you aren't there all the time, I think running electric will be cheaper in the long run than restocking the pond a few times, not to mention the years of fish growth that you lose every time they visit.
You will need to either turn kill the power to the fence when you are physically at the pond, or set it back far enough from the water that you can walk around it easily. If it was mine, I'd just cut the power when I was there and put a lighted switch so that would remind me to turn the power back on before I left.
