Hi M.,
I am an RN too and I'm sorry you seem to be having problems with night wetting. I too had the same problem with my middle daughter. Is he a heavy sleeper? They seem to be the ones who most trouble with getting up at night, since they sleep so heavily they do not wake when wet.
We did try the underwear alarm, but since she slept so soundly it really needed to be a firetruck siren for her to hear it. What finally helped, and I know it is hard, but we finally just did the "two-week" method.
Most of the time, they are good until the first hour after they are asleep, that is usually when they are relaxed and release their bladder. So, you have to wake them an hour after they are in bed and have them urinate. Then you set your alarm for another two hours and wake them again. Do this in two to three hour intervals until morning - and you can get a good idea of how long they are usually dry. You have to do this for two weeks straight to get their systems used to waking at night and going to the bathroom.
Yes, I know this is difficult, but it does take time and patience. We tried at four the first time, but she was not ready. We tried again at 5 and it was a success. We had to do the same thing with her thumb sucking and both methods worked.
Good luck M.!
M.