How do I secure the Firewire cable on my MacBook Pro?
It is very low tech, but some tape is both cheap and effective at holding a cable securely when you start the tape around the cable and then have an inch or two of tape holding the cable securely along the bottom surface of the mac.

Choose one with adhesive that cleans with alcohol and most cables and bottom cases are safe for cleaning any adhesive residue that may remain after your session.

I have also seen people use velcro cable wraps with the hook portion affixed to the cable and a loop pad semi-permanently affixed to the bottom of their MacBook Pro. The loop isn't that disruptive in daily use and you only have the hook portion of the velcro on the cable so it can be tucked away when not in use. This is far superior to tape or rubber bands for a more heavy duty connection under repeated use cycles.