I'll briefly agree. Random is not an appropriate word in this context when there are people making choices about who to stop and who not to stop. People are not random. They have thought processes that are sometimes legitimate and sometimes biased, and sometimes unconsciously so. All of that will come out when you give police officers unfettered discretion.
In terms of the defences, I defer to my colleague, the defence lawyer, who's in court.
With the drug-impairment and the legalization of marijuana, there is still a lot more work that needs to be done on what an effective drug-impairment regime looks like. Some of that work is scientific work. The legislature cannot jump the science. You cannot push beyond the science.
I think that trying to pass a comprehensive reform of impaired driving provisions while you have an enormous outstanding question related to drug-impaired driving doesn't make a lot of sense. If you're going to comprehensively reform impaired driving, then you should do it in concert with the science and do it once, so you get it right one time and you do it in the best way you can.