Damn a beaver.
Kill the bastards.
They won't go in a box trap, they are dumber than shit, but not that dumb.
Your best bet is to call the wildlife commission and report them. If its illegal to build a pond in your area, then those beavers are in big trouble. Collect copious amounts of evidence of their scofflaw ways. I also recommend posting signs, notifying the beavers of the particular statute that they are violating. Also let them know the location you want them to relocate, and assure them, there will be no further action on your part, if they build the pond to your specifications in the new location.
These actions should result in a tenable solution.
If not, hang some snare wire around their lodge in the shape of a noose. Theyll get the message or else.