You could try the barrel set, make sure it's legal (I think it is).
BARREL TRAPS. Fifty gallon steel drums with sides perforated from
the base to the center with the tops cut out and replaced with a plastic
cover slit across the center.The barrel is weighted with rocks and submerged so
that eight or ten inches extend above the water level. An inclining
board from the water or one placed from the bank provides access to the
top. Muskrats lose their footing and slip through the slit area and
are then drowned. I have seen them with a couple of wooden ramps
as well as something to hang a piece of bait like a carrot or apple over the
slit in the tarp.