I'm not a policeman, but I thought that the various police forces around the country would have at least a couple of 'crime prevention' officers.
Find out who yours is, and point out your neighbour's house to them. They'd be only too pleased to pop round and give him some sage advice. (Actually, they'd probably think it a PITA detail, but still....)
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Years ago (40+), our neighbours were burgled during the day. I was in at the time, but didn't hear a thing. The first I knew, was a uniformed officer at our front door, asking if I'd seen/heard anything, and suggesting I check over our own house, they suspected the crim was still in the area, (I was 13 or 14 at the time, just bunking off school). I took our two dogs (Rough Collies) with me and went around the house, checking windows and doors.
I was upstairs, when I heard the back door being opened. "Hello? Hello? Anyone here?" the voice from downstairs called. Since they didn't identify themselves, I kept quiet - to me, the burglar had snuck in, looking for somewhere to lay low.
The back door closed again. I snuck downstairs, keeping a tight hold of the two dogs. No-one there, I crept out of the back door, and saw the back of a man, peering into the side door to our garage. I released both dogs with a cry of "Kill!", and Storm and Amber leapt up at this bloke, who promptly fell-over into the now open doorway, with both dogs on top of him.
Quite a large commotion, with not a few expletives filling the air, and suddenly our back garden was full of policemen, mostly uniformed, but some, like their hapless colleague that our dogs had just attacked, were plain-clothed!
Needless to say, I got a lot of 'Well-dones' from the blokes compatriots - and he took a lot of justifiable stick, for not identifying himself when he first came into our house!