Both Bitter Apple and alum work if properly introduced. By spraying it on something the dog has already formed a 'chewing attachment' to won't work. The dog gets a reward out of chewing the table leg or whatever and so will suffer through the bitterness. After all, that varnish probably didn't taste so hot either. Think of it as similar to when people speak of "acquiring a taste" for liquor, soda, certain foods, etc.
To get the best results, soak a cotton ball with the spray (either one) and wait until the dog is just hanging around, watching TV with you or so. Walk past him and sqeeze the cotton ball so the liquid is squirted into his mouth and watch how much he tries to get the taste out! Since it was introduced in a neutral manner, he has now formed an association that "bitter apple =YUCK". If you think you have a 'tough-tongued' dog, you might try it once more on a different day. The next time he goes to chew whatever it was (table leg, couch cushion, etc), he'll smell the spray and remember how awful it tasted and should leave it alone.
If you have already tried the Bitter Apple and he still chews, you probably won't be able to get the BA to work. Try the alum spray or something else.