Do you have an overflow pipe coming thru the dam from the surface of your pond? A client uses a MB650 trap right before his and catches a couple of otters per year.
Snare or conibear on the pier, I can only think about putting up a short fence (12" high or so) out of chicken wire, snow fence, etc. and leave some openings in the fencing for the otters to go thru. Put snares or Conibears in those openings. Watch for any pets though, they will be dead if they try to go thru the openings.......
