I figure that for a few thousand dollars and a spare laptop or two I could have a system very resistant to cutting phone or power lines, and something which would make surreptitious entry teams think twice. (Leave a couple of the 802.11b cameras visible, put another behind a Lexan plate, etc.)
802.11b can be jammed very easily; simply by having an 802.11b card with a really powerful amplifier (just sniff the traffic and find which channel it's transmitting on, then transmit garbage at 50w). Best to have regular ethernet backup channels in at least the most important cameras. Of course someone would need prior knowledge of your system, but I think with the level of professionalism you're talking about we can assume a decent amount of time/effort put toward surveillance.
