To answer some other comments I haven't specifically picked up on thus far.
I did have him in the house when I was out when I was first here, and it worked well for up to four hours. I didn't want to leave him longer in case he needed to toilet. Then one day I got waylaid, it was longer than four hours and although he hadn't messed thank goodness, he had done some damage to my rucksack, in which there were some dog biscuits I guess he could smell. Unfortunately after that, he started investigating and causing damage even when left for shorter lengths of time, and when given a good walk beforehand so should have been happy to sleep for a few hours.
I have a small cage in the house but don't like to leave him in that for very long at all, it's just large enough to stand and turn around. There isn't room for a bigger one indoors. The other dog often chooses to be in that cage when she's in the house with me, but she's not shut in it and I'm always present. (She's not reliable in the house on her own, but is fine if I'm in.)
The cage I do leave Skip in is a very large one but one of the things that bothers me about leaving him for a longer period is that I don't like to leave water in it in case he spills it and then is lying in wet, which would make him very stiff and uncomfortable.
Yes of course he deserves a good retirement, and he'll get one if it's practical. He's his own worst enemy, with the destructiveness if indoors alone, barking if outside, and being so horrible with children. Apart from all those things, he's a lovely dog

. But arthritic, which also constrains how and where I can leave him.
Juliet's idea of having him with me while milking did make me think about whether there are times they could be with me but aren't, but I do spend as much time with him as I can, often being in my own space in order to be with the dogs when in fact I would rather be out with other community members, but I can't be with him
all the time. If I'm out and about on the farm, the dogs are usually with me unless it's unsafe or I'd have to leave them tied up, which they hate. As to milking itself, even if I did the hurdle pen thing, and made another pen outside the dairy for him to be in while I'm getting ready for milking and when I'm processing the milk, I couldn't manage a dog on a lead plus carrying all the gear to the field and then the milk back to the dairy. We only milk once a day, first thing, and usually the kids are having their breakfasts and aren't out and about just yet, so it's not the worst time for the barking anyway. Some days I am in the dairy for some time later in the day, and I can certainly think about making a comfortable, weatherproof pen for him outside the dairy, so he can be near me (and away from the children) when I am in the dairy.
We had a lovely long period of peace when the neighbours' garden was unappealing to children, and the space in front of the decking had enough foliage to provide quite a bit of screening. After the 'princess castle' got moved elsewhere and before the recent digging work opened up the space and made a lovely spot for the kids to run around, have a slide down a bank, and so on. Just my luck it's within sight of my decking and also the outside kennel. It doesn't feel appropriate to ask the children to not play there, especially as that family has three boys, two of whom are very keen on being indoors on their computers so we are all very pleased at anything that gets them out in the fresh air! Moving Skip to a different location now, not near where he knows I am living, would be very unsettling for him, I think.
The suggestion of someone coming up onto the deck and spraying him in the face with water when he barks is, to me, worse than the vibrating collar. The latter gives him an unpleasant feeling if he barks more than a couple of times, enabling him to choose to be quiet and be comfortable. The spray bottle gives him the experience and thence expectation that people he doesn't know very well may randomly approach and do horrible things to him. The decking is up some steps, and he stands at the top of the steps barking. If he stops barking as the person approaches, then they would be spraying him when he isn't doing anything wrong. If he is still barking, then he is seeing them as a threat and is guarding my house, and is attacked for so doing. Thankfully he generally likes most adults, but he has been known to nip people he doesn't like, so teaching him that anyone might do horrible things to him at any time seems to me to be a recipe for a much more difficult dog than I already have!
i will continue to work on things that should reduce the problem, and some of the ideas in this thread have been helpful so thanks everyone for the thoughts.
However I remain of the opinion that some discomfort as discouragement is preferable to having to be incarcerated where he can't see out (which clearly upsets him), being PTS or biting a child and then having to be PTS, so I think I will get one of the vibrating collars and see how we get on with it. I will report back.