I totally understand why you'd like to keep him in the crib.
I know this will sound simple, but have you talked to him (your son) about it? Our daughter climbed out when she was about 22 months and fell and cried. We all told her how lucky she was she didn't get hurt, and how it was super dangerous to climb out of the crib, and how if she needed out to call Mom or Dad or Grandma if she wanted out but not to do it herself. We talked about it and stressed this message for a couple of weeks and she never tried it again. Of course, we also had a video monitor so we could watch her and when she called, we would honor our part of the bargain and go in. We moved her to a toddler bed when she was 3 years and 4 months. It was awesome and an easy transition as she was ready. At 22 months I am not sure it would have been easy for us.
I have heard of people using the crib tents happily - we have a sleigh style crib and it didn't fit.
Good luck.