If three riders were at the tapes at 7:30pm Harris would've been disqualified. It was agreed to delay the meeting for fifteen minutes, so the problem never arose of him delaying the start of the race.
They used to sample every greyhound for testing but as you say costs were prohibitive and it is now random sampling. Sometimes before a race and sometimes after as the person parading the dog could addminister something.
To ianb. It's not tracks can't afford sawdust, it does grow on trees you know, but they're not allowed to. Thanks to the enviornmentalists for that, same with dropping oil onto the track.