Get a nuisance beaver control permit. Can't remember how long they are good for, I think it is 45 days or so and you can. I had to do it last winter on my parents property. Trapped 2 of them.
Break open a reasonable size hole in the dam so the water level will fall substantially and retry your hunting. They will be there quickly to try to repair the hole.
17 HMR
I too am a long time fan of the HMR (Savage 93). I found that switching to digital night vision (photon xt) has cut shot distance considerably at night when I'm fox hunting. Some distances my Gamo Whisper could've handled! If there's a chance that a shot will be longer than 75 yrds, I...