Absent international treaty or a national law (assuming their competition can be assailed in the court system), anyone with a plan like this will be forced to defend their claims the old fashioned way: by force. Will the beacons have probe-disabling lasers on board? The article doesn't say. But my guess is that the cost of getting a defense system on the rock is the same as the cost of getting mining equipment on it.
A better defense plan is to scan 10 times as many rocks as you normally would and leave beacons on all of them. Then develop either stealthy or very fast mining tech for phase 2.