Transparent added on time.
Time wasting is an absolutely massive problem. (1) Even if the ref adds on the right amount of extra time, once the clock reaches 90 there seems to be an added desperation in the team that is losing that is not compensated for by adding on time. (2) Refs never add on the right amount anyway, in some cases they are many minutes under.
Solution: have the ref's watch run the stadium clock. This means everyone knows firstly exactly how much time is left and secondly exactly how much time has been added on and when. If refs were seen when and when they don't add time on, it would be a great incentive for them not to be conned by the cheating (for that is what it is), and apparently giving more time to certain teams, less time to others. They will probably say they don't, to which I say fine, if your match watch was in the public domain then you can prove how unbiased you are.