I get your point about not leaving bikes unlocked - that would be tempting fate. I hate it when bikes get vandalised though - it's so sad that people will get a kick out of depriving somebody else. There's not even a profit motive, just sheer malice.
I'll definitely be checking out Mags. I hear it's a very beautiful area. I'll need to work on my surfing a bit before paddling out there though - I haven't surfed in 3 years (since living in London) so I ain't so hardcore anymore. I'll be checking out the city beaches first I think