I feel for you! Since buying our 80 acres complete with 9 acre pond and one heck of a beaver issue I know what you're either going or going to go through. I've whacked 27 of them so far in a combination of shooting and traps.
They're not that hard to shoot, but they are a smart and adaptive foe. Usually best time for shooting is early am or dusk. At dusk they seem to have this habit of surfacing from their den, then going on "patrol" around the pond perimeter to check things out. Excellent time to ambush them. Try to get straight on shots as compared to broadside, way more room for error. IF possible, let them exit water as it's a much larger target. I use a HV .223 varmint bullet that will fragment when it hits water unlike .22LR that will ricochet. For a rifle I use a REM 700 XCR compact tactical with a Leupold 6.5-20X MK4 with illuminated reticle. Little bit of overkill, but I'm constantly whacking muskrats too. Once you whack a couple beavers, they'll shift times on you or go completely nocturnal. Then I switch to a shotgun #1 or #4 buck with a tac light.
Trapping is far and above the best, most efficient way to get them. I use 330 conibears on runs and dens, but prefer leg holds with drowning slides. I normally set a daisy chain of a couple leg holds per set "protecting" my drain tube. Then a few others in runs where I can see they're feeding or moving through during their "patrols".
Also looks up a thing called "Beaver Deceiver".
http://en.wikipedia.org/wiki/Flow_device
It's a fence system for around the drain tube that confuses them somewhat, and allows water flow even if they dam up the cage.
Scent mounds do work pretty well throughout the year as the little buggers are territorial. They can get them to investigate into your set just to insure a new beaver hasn't moved in.
The other solution that finally worked for us was to remove all of the unwanted vegetation (trees) from our pond banks and protect the ones we wanted to keep with cages. No food = no beavers. I also got permission to hunt/trap the pond up stream, which we nicknamed "Cambodia" cause they were using it as a staging area into our place. Between the two, we've been beaver free for a couple years now...
Good luck!
Chuck