Overnight damage isn't likely to be caused by squirrels since they're diurnal.
"Because squirrels are diurnal (active during the day), it is usually pretty easy to see for yourself if squirrels are responsible for damage to plants and vegetables. And, of course, if you know the damage occurs at night, you can rule squirrels out entirely and should focus your efforts on nocturnal animals in your area, such as raccoons and opossums."
http://www.peta.org/issues/wil...
We get damage here in spring and fall; for limited amounts of time. I just cover target plantings with plastic mesh or tulle until it seems that the crisis is over.
Products containing blood meal probably won't be as effective since a lot of troublesome nocturnal scavengers are omnivores, but I'll second goldfinch4 and say that you might check out a repellent product called Plantskydd.
For reducing squirrel and chipmunk damage in containers, you might try placing rocks around your plants.
