This is an interesting thread with lots of conflicting advice and anecdotes. In short, I think you’re probably both wrong and that DS does sometimes wet himself on purpose BUT he’s not being naughty.
Here’s the long version of my POV as the mum of an autistic DS who was very stubborn & prone to meltdowns as a toddler:
To the pp who said a S&L therapist’s opinion is on a par with that of a random guy in a grocery store – an S&L therapist is one of the 3 experts (the others being a paediatrician and an Educational Psychologist) who perform the multi-disciplinary assessment on a child to determine whether or not they are autistic. Their opinion is definitely worth taking seriously.
If he has a speech delay, he may well be more reliant than other 3 year-olds on other methods to help communicate what he wants – some of these might be undesirable behaviours such as pushing, hitting and protest peeing. Working on communication is key. If you need to say no to something, do talk to him, acknowledge his feelings and explain (concisely) the reason. This doesn’t mean pandering to his every whim but he does need to feel heard (otherwise he’ll keep asking!).
The saying goes, ‘When you meet one person with autism, you’ve met one person with autism’, hence why there are wildly differing experiences on this thread. My DS was definitely capable of holding his wee and doing a protest wee at the age of 3. He wasn’t being naughty, he was trying to communicate to me his feelings around potty training – I think it was that he was angry about the change being out of his control and he was worried about getting it wrong.
A pp mentioned the EarlyBird parenting program (designed for parents of autistic DC) – I did it with DH and it was really helpful. Learning about the importance of routines, letting DS know what’s happening in advance, spotting meltdown triggers etc
DH is definitely approaching this in the wrong way – anger and force will get him nowhere. You both need to deal with the bad behaviour in a patient, calm, gentle but firm and consistent way. And if he’s having a meltdown, he’s beyond being reasoned with – if the music doesn’t work each time (well done on that one btw!) put him somewhere safe where he can let the frustration out and calm down. Don’t react or tell him off for a meltdown – it’s a sign he’s overloaded and lost control. Try to find out what his triggers are and look at ways to avoid them. As pp just suggested, distraction before escalation.
It won’t always be like this but do try to get your DH on board or it will be a tougher few years ahead than it need be. Best of luck OP!