How can I fix my outdoor security light which is stuck on?

I have an outdoor security light which hardly ever comes on (which is fine) but it is now stuck on! As we have had snow today I have wiped the sensor but notice that the thin piece of fabric there is torn. I really need to be able to turn it off but there is no switch other than the one for all the lights in the house at the fuse box. Any ideas please? Thanks in nticiption.
Robert