Nothing to do with six-seventeen; I've heard 2 versions:
1. Due to a spoof played on him as a JP. Something about being told to look after the boss's dog which was then kidnapped by his chums and he was told that it had died - so he was going to have to explain that to the boss.
2. A less charitable version was something to do with the sense of humour of a dead dog.
During SSC's time, I understand that the 'Dead' part was dropped as it rather tempted fate.
Anyway, good luck with poling 'Bloodhound'!