It sounds as though your son is ready to be trained, and it will probably go fairly easily now that he doesn't like to be wet. If you live in a place where neighbors won't criticize, I wouldn't hesitate to let him urinate in the backyard. Since he tends to hide behind something, let him hide behind a shrub or piece of lawn furniture.
When my son was about the age of yours, he didn't like to use the potty because he was always too busy to stop what he was doing. If we were out in the yard he would rather wet in his pants than stop playing and go inside. But he was happy to go â€œbehind the hollylocksâ€?—his word for hollyhocks—so they got a lot of extra urea in the soil, and it didn't hurt them a bit. In time, he gave that up and went in the potty. So you might want to give something like that a try as an in-between step.
As far as sitting versus standing goes, it doesn't seem to make much difference. Little boys often miss the target, whichever approach they use. If he could observe his father and then be encouraged to act accordingly, it would probably help.
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