That is such a difficult situation to find yourself in.
I do hope your neighbours, having known your husband in better times, are able to see the situation for what it is and it hasn't damaged your own friendship with them.
I am at a loss at what to suggest. Is the boundary fence yours or the neighbours? I am wondering, if it is yours, you might be able to replace it with something that provides more privacy and would benefit both sides?
I haven't experienced the kind of behaviour you have described but, as my husband is spending more time in the garden I am considering putting in a higher fence on one side (the other side already has a high fence). This is because I am worried about him climbing over the smaller fence - or, as time goes on, acting inappropriately in the back garden.
One lady I know is mortified that her husband, who has Alzheimer's, often exposes himself to wee in the back garden and she is worried someone will report him for indecency.
If you already have a high fence would it be possible to grow foliage which will grow dense enough to keep your husband from getting right up to the fence so that he can't hit it with bricks or anything else? A bit late this year, I know, but maybe something that will take by next year?
We get on very well with our neighbours, they have also had experience of dementia in the family. It's nice to say hello to them over the low fence from time to time but in the long run, I think a higher fence and some nice foliage would be beneficial to both sides, especially as they have a small child to think about too.