Hi C.,
OK, well I read the other suggestions you received & have a much easier method to offer...my son is 3 1/2 and successfully potty "trained"...he showed interest at 17 months & just only finished up this past fall when he started preschool. So if you do the math, that's a LONG time to be working on it.
We tried so many methods, and the things that worked were to get rid of the pull-ups & go back to diapers, first of all. Pull ups are expensive, & too much like underpants. We thought it best to not try to simulate underpants that he can pee in.
We bought & read several different types of potty books on a regular basis. (even after he was potty trained, he loved reading them so he could say "I am a big boy now!") We talked about the fact that someday he would be ready to wear big-boy underpants like the boys in the books, & like the bigger kids we know, & like Mom & Dad. I resigned myself to the fact that by age 20, he would be potty trained, and stopped trying to make him do it on my schedule. I just took my effort out of it, and made it HIS choice. He would want to play using/wearing the big boy pants, but I told him those are special pants & he can only wear them when he is done with diapers.
To my delight, this seemed to take a lot of stress & negative energy out of our interactions, as well as make my job easier as I didn't have to devote a weekend or holiday to "potty drills", nag about it, or clean up constant pee/poo messes.
We knew he wanted to go for a ride on our boat (my husband's fishing boat), so my husband & I told him when he was all done with diapers, he could go for a ride on the big boat, and we'd have a party with cake to celebrate. Boy was he excited after that! We kept telling him, when he's ready, we are looking forward to that cake party on the boat.
Then one day, after he had been keeping his diaper dry pretty consistently (he still would go to the potty most of the time), he told me he was ready to get rid of the diapers. And he did, and he never went back! It coincided with starting preschool, where most of the kids (age 3-5) were potty trained. But we think what kicked him over into really doing it was the incentive of having a ride & a cake party. We did the party the soonest we could, and made a great big deal of it. Fun!!
Maybe you can think of something your child would really love to do, and hasn't done yet, and make that as an incentive....be creative, have fun and try a different paradigm than being a drill sergeant!
It's a lot easier, less stressful, and we even gave ourselves permission to chide/tease our boy a bit about being too big for diapers, & how we'd really LOVE to not have to buy diapers anymore, but also said with that talk that he will do it when HE is ready. (he is used to our teasing, which is done with a loving attitude, never to humiliate or belittle him...he even learned the "rules" of teasing, which he now does to us too)...which when he was out of them, he loved to remind us that we can't tease him anymore!
Hope this gives you a different perspective. Have fun!