I don't know if you have to reapply it or how often, but I'm pretty sure that it tastes horrible even if it dries onto the material before it's licked or taken into the mouth. When my first dog kept chewing on the leash, I soaked the leash in Bitter Apple, and even after it dried he didn't bite it.
Have you ever tried tasting it? You can put just a drop on your fingertip, and bring it to the edge of your tongue. It's nasty. Or you can dilute a little bit in a cup of water, juice, soda... Either way, don't say I didn't warn you.