Can Find My Mac be blocked?

Hi,

I'm just curious whether Find My Mac can be blocked...what if a person stealing a computer installs firewall software on the computer that blocks all connections to iCloud.com? I'm trying to avoid turning on FileVault because I had disk corruption on my last Mac and it was a nightmare trying to pull some of the files off of that computer. At this point, I turned on Firmware Password and feel inclined to weld the screws keeping the computer case shut to give an extra measure of security, but that would probably void the warranty. There is a thick metal lining on my desk that cannot easily be cut through and it would take too long to try to remove the desk from the house (each door would have to be taken off its hinges) for that to be a practical option for anyone, but there is no Kensington lock on this model so I have to think of another option.

So, what is your advice in securing my new Retina MacBook Pro?

Chris