Please try the ideas in these links:Inappropriate Peeing Problems Answered (click here)THE LITTER BOX FROM YOUR CATâ€™S POINT OF VIEW (click here)
Did the vet take a urine sample and check it? If not, I'd take him back and ask for him/her to check the urine sample, to rule out crystals or infection. Unless urinary problems are completely ruled out, it won't help to try behavioral measures- if crystals or infection are present, it makes urination painful and causes aversion to the litterbox.
Please don't stick a cat's nose in its urine if it goes out of the box. When a cat goes outside the box, it's trying to tell you something is wrong - either the cat is ill, or stressed, or there's a problem with the litterbox. Punishment won't solve the problem, and will only cause your cat to fear you - and possibly just start going where you're less likely to find it, in a hidden corner or closet instead.