Hopefully the arsonists would act in a bush league uncoordinated way so that acccess could be restricted.
My fear is a team setting 50-100 fires in a line in two hours. There would be no time to see the total picture until it was a fait accompli.
Another preventive action would be to cut firebreaks now. Highways and bare ground act as firebreaks. Put fairly wide roadlike clearings everywhere we might want to stop a fire. Don't even let it be possible for a fire to burn more than a few miles before it runs out of fuel. And keep the firebreaks clear from now on. It would also make it much more difficult for terrorists to sneak around.