Potty training can be hard, especially since they would rather not stop what they are doing to go to the potty.
My 22 month old daughter is almost completely trained (still working on nighttime, having about 1 day time accident a week). I put her in trainers at 18 months during the day, because I think it's important to show they them you believe them able to do it. I also think it helps them learn to read their body better. I put her on a strict schedule and just praised her like mad. When she was really resistant, I brought out stickers. What I found helpful was to stop asking. Instead, I just tell her we are going and ask her questions," are you going on mommy's potty or on yours?" "Am I carrying you to the potty or are you walking?" (I use the later when she shows some resistance.) I then start acting silly, and the distraction usually works.
I know many people would tell you to just wait until "he is ready", whatever that means. I tend to disagree with the more recent idea that kids aren't ready till they are 2-4. 90% of kids were trained by 18months prior to 1960. I think potty learning is like many other developmental milestones that require guidance and assistance (think of all you did to help your son walk?) There is a lot they need to learn to be fully trained. As parents, it's our job to make the process fun, but to assist them as they learn it. If they know the difference between wet and dry, and have the physical control to go on the potty, then they are ready, and it is then our job to help them be successful, Since my daughter has become almost totally successful, there is no resistance. She is proud of herself. I think a lot of the resistance is frustration on their part. They know what we want them to do, but they just don't totally get it. To get it, they need to practice. So, yes, be tougher if that means putting him on a schedule. We had rules in our house: we go first thing in the morning, before we leave the house, etc. When we established the rules, hubby and I showed her the rules.
When he starts to have some serious success, ditch the diapers, and get him some gerber trainers that contain most of the accident.