No you cant prove innocence but you can do your best to remove the doubt.
Agree with that, although you still have to deal with the paradox. Really looking for doping means finding doping. Like I said, it's questionable if you'll succeed to remove the doubt. It's the hard way, but the only way.
There has been a decline in the number of tests. A few riders have commented. Why is there not an outcry from the peloton who are sick of seeing mainstream media only write about doping in cycling? Are they that stupid, no why because they dope!
There has been decline in testing, yes, according the UCI due to more targeted testing. Which could be right (it's probably not coincidental that the riders who ring the alarm are the ones that are less tested, for that matter) although there have also been mentions of races where has not been tested at all - which would be problematic...
For the second part of your remark, I think it's a different question. There have been lots of guys who told they were sick of seeing mainstream media only write about doping in cycling. Andreas Klöden even boycots the German media, and that says it all, isn't it?
To clean up the sport it has to start with the riders. UCI is not gonna do it. Teams run by the likes of Bruyneel, Riis, Gianetti etc are not going to do it, so it needs to start with the riders. Not easy I know but they will be the main beneficiaries.