This isn't Unconditional Parenting, though. I used to think it was ridiculous nonsense, if I'm honest, but now I've read the book (not really planning to apply it wholesale, but definitely a useful read) I actually agree with a great deal of it. It talks about how you have to say no so very often to a child, to stop them damaging themselves, others or objects, that you should perhaps consider when you're saying no as a reflex habit rather than for a good reason. Damaging someone else's property is a good reason! It discusses trying to be honest with a child who is old enough on why a no is being given. An example is where they want to watch something unsuitable and say all their friends are. A common (my own, if I'm honest) response is the old "would you jump off a cliff..." which is actually pretty silly, and the child knows it, even though they generally can't articulate why it's silly (because it's an irrelevant, dishonest and facile comparator). Agreeing that it might be quite hard to be left out and you're sorry about that, but you think some things are just too violent/adult for someone that child's age to watch, because they're learning about the world and their own place in it, is still "no". It's just a more honest one, and by being honest it actually treats the child better and makes it seem less like an arbitrary and unfair imposition. The answer's still the same.
A friend UP, and their ds wanted Coco Pops for breakfast. Which is basically junk food. They said no and explained why, but offered to buy the Coco Pops as a pudding after meals, like any other sugary crap. That was honest, definite, and yet allowed the child a compromise. I dunno about unconditional, but it seemed thoughtful. It also reinforced sugary crap being a treat food. The thing I do like about UP is that it addresses why the child is doing whatever it is doing, whether that's negative or positive. The theory is that rewards and punishments can train them to want the rewards and evade the punishments, rather than be rewarded by making their own lives easier or enjoying being a nicer person, and penalised by knowing they've hurt someone or made themselves unpopular, IMO. It makes more sense to make the rewards of a behaviour stem from that behaviour - nobody's going to be armed with a sticker chart or a naughty step when you screw up or succeed as an adult. And I don't buy that making a child howl in misery is going to make them feel remorseful about bad behaviour. When I was small it just made me miserable and filled with rage. I can't see that as especially useful in teaching a child better ways to behave. Interestingly, my mother has found it really helpful, too, as she said a lot of the antagonism and rigidity she thought she had to use to be a "good mother" felt absolutely wrong and seemed very counter-productive. She feels that UP makes sense to her, having brought 2 kids up as a single parent.
I think there's a gulf between UP, which tries to treat the child with respect and honesty, and where you try to model the kind of behaviour you hope they learn while encouraging them to understand the reasons why they should behave well, and bringing up a spoiled brat. Allowing your kid to trash someone else's property is the latter, and when they aren't even 2 how on earth are they meant to know any better, anyway? Surely removing them from the situation and then distracting is wise?