C.F.
From Sally Beauty supply there is a nail polish called "no bite". I believe Orly makes it. I use it on my husband all the time. It's VERY bitter...so when they bite subconciously (sp?) the taste is there and deters it. the polish will last at most 2 days on the nails depending on wear and tear.
Something similar can be found at Walgreens, and it's in the baby section. Not sure of the name though.