So what's the solution ? Assign a surveillance UAV to every Russian ship parked "without a good reason" over a cable ? It would be expensive, but doable, and create a reserve of vehicles for wartime use.
The solution is to project strength and hit them where they don't expect. You are dealing with a thug, not a cost/benefit accountant, as Obama seemed to mistakenly believe. As long as they do things and we respond, nothing good will happen. They have already calculated the response and found it acceptable. Instead of this, go to the mattresses. Oh, your bridge has suddenly exploded? Shame.