Secure storage during weddings for wedding photographers

I would like to buy a bag in which I can securely store my lenses and back up cameras during weddings. What do you use?
I know assistant is the solution who can watch your bag but a lot of time is is just not feasable. Also, I can carry all the cameras and the lenses on me but it is impractical a lot of times...
What I am looking for is something which is hard to take from the without somebody noticing it and I can lock it.
Somebody suggested that I can get bags which have an alarm...
It would be great if I didn't have to worry about my stuff all the time.

I appreciate your help!

I suggest you consider the Pelican 1510 case http://www.pelican.com/cases_detail.php?Case=1510 ,I have one and the potential thief would need Semtex (plastic explosive) to get into it.