My Westie is licking one of his paws, to the extent that all the fair on his foot has gone, and his paw looks red.

I had some nasty tasting spray, that we have tried on him, but its obviously not nasty enough, as it has'nt stopped him, and infact seems to stay in my mouth and on my hands for days.

His paw is not sore, as he'll let you touch it, but, as said above nearly all the fur has gone.

Any ideas on how to stop this?