One of the dens almost went to the middle of the dam.
Keep an eye on that one even after the beavers are gone. We had a den like that once and after the next big rain a hole popped on the backside of the dam where the den was. We had to drain the pond down two feet below normal pool and then had to have a bulldozer come in and repair the damage, it wasn't cheap. Did you happen notice an air vent hole on top of the dam?
Those 330 conibears work quite well, so do .22 lr and 000 buck.
