Yep otters and raccoons... Every one has excellent ideas... My friends use 5 gallon pails with screw on lids... drilled a bunch of holes in them and split the minnows, put a sizey rock in the bottom to keep it on the bottom and wire the lids for the critters and you should be good... always going to lose some, even the bait shops do. If you are bringing more to stay out bring another bucket... oh and make sure you tied the bucket off...

Mark