Building there was a zoning violation anyway. Think of it as random and overwhelming enforcement of municipal ordinances!
On a serious note, simply having the transmitting electronics powered by a coaxial beam from the receiver (that is itself initially powered by a low power pilot beam from the satellite) seems like it would be an effective interlock to prevent a wandering beam.
From what I've seen, though, it's difficult to make a very tightly focused beam that doesn't lose much of its power to the atmosphere. It's more efficient to use a diffuse downlink beam and a large collection array at the ground, so a wandering beam wouldn't really do much damage.