I know i contradict myself, as i did think that posibly a rule where the race leader cant use it unless the guy behind is within a second of him? So Vettel would have to wait till Alonso was up with him more or less before he could use it. The the leader could use it for defence, meanwhile the attacker still had his usages left.
This way it would be used for Push To Pass purposes.
Another thing this would also do is increase fuel consumption of the leader as he wouldnt be able to run and hide any longer as he could be attacked later in the race. Teams would have to run with more fuel in the car for this eventuality if they needed to turn the wick up a little to try and defend in the last few laps.
Another thing id also do for safety reasons is make it that if a driver was to input more than 20 degreese of action into his steering the flab closed, thus meaning the tunnel at Monaco would be usless and the likes of Eau Rouge or Blanchamont would also be usless.
It would mean that drivers could use it in many senarios, thus negating the undercut of new tyres, maybe make DRS disabled the lap after a pit stop as well.
One thing id posibly do is make Monaco and posibly Singapore a Non DRS race for saftey reasons. Or in a Street circuit have only 10 activations per race and the usual 3 for Quali.